- Email: [email protected]
Arthroscopic Quantification of Syndesmotic Instability in a Cadaveric Model
Arthroscopic Quantification of Syndesmotic Instability in a Cadaveric Model Ross Feller, M.D., Todd Borenstein, M.D., Amanda J. Fantry, M.D., Roy Bradley Kellum, M.D., Jason T. Machan, Ph.D., Florian Nickisch, M.D., and Brad Blankenhorn, M.D.
Purpose: To investigate whether arthroscopy or stress radiography can identify instability resulting from single-ligament injury of the ankle syndesmosis and to determine whether either modality is capable of differentiating between various levels of ligament injury. Methods: Syndesmotic/deltoid ligament sectioning was performed in 10 cadaver legs. Arthroscopic evaluation and fluoroscopic stress testing were completed after each sectioning. In group 1 (n ¼ 5), sectioning began with anteroinferior tibiofibular ligament (AITFL), then interosseous membrane (IOM), posteroinferior tibiofibular ligament (PITFL), and deltoid. In group 2 (n ¼ 5), this order was reversed. Measurements were made by determining the largest-sized probe that would fit in the anterior and posterior syndesmosis. Radiographic parameters included tibiofibular overlap/clear space and medial clear space. Results: No radiographic measurement proved useful in distinguishing between intact and transected AITFL. Anterior probe (AP) size reached significance when distinguishing between intact and AITFL-transected specimens (P < .0001). AP detected significant differences comparing single with 2-, 3-, and 4-ligament (AITFL, IOM, PITFL, deltoid) disruptions (P ¼ .05, <.0001, and <.0001, respectively). Significant differences were observed between 2- and 3/4-ligament (P ¼ .02) transections. Posterior probe (PP) size detected significant differences between intact and single-, double-, triple-, and complete ligament transections (P values .0006, <.0001, <.0001, <.001, respectively). PP detected significant differences between single- and double-, triple-, and complete ligament transection models (P ¼ .0075, .0010, and .0010, respectively). PP distinguished between 2- and 3/4ligament (P ¼ .03) transections. Conclusions: Stress radiography did not distinguish between intact and single-ligament disruption, and was unreliable in distinguishing between sequential transection models. Arthroscopy significantly predicted isolated disruption of the AITFL or deltoid ligaments. Also, probing was able to differentiate between most patterns of ligament injury, including sequential transections. Clinical Relevance: These data can aid surgeons during arthroscopy of the ankle when attempting to correlate intraoperative syndesmotic evaluation findings with the extent of ligament injury.
I
njury to the syndesmosis is common and occurs in up to 11% of all ankle injuries.1 These injuries can be purely ligamentous or may be associated with fractures,
From the Department of Orthopaedic Surgery, The Warren Alpert School of Medicine at Brown University, Rhode Island Hospital (R.F., T.B., A.J.F., J.T.M., B.B.), Providence, Rhode Island; Capital Orthopedic and Sports Medicine (R.B.K.), Flowood, Mississippi; and Department of Orthopaedics, University of Utah (F.N.), Salt Lake City, Utah, U.S.A. The authors report the following potential conflicts of interest or sources of funding: F.N. receives consultancy fees and royalties from Smith & Nephew and has stock/stock options in Connextions, First Ray, Surgical Frontiers, and Mortise Medical. Received October 26, 2015; accepted November 3, 2016. Address correspondence to Amanda J. Fantry, M.D., The Warren Alpert School of Medicine at Brown University, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903, U.S.A. E-mail: [email protected] Ó 2016 by the Arthroscopy Association of North America 0749-8063/15986/$36.00 http://dx.doi.org/10.1016/j.arthro.2016.11.008
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and they can be categorized by the Lauge-Hansen classification system.2,3 Injury to the syndesmotic ligaments may cause instability of the ankle, leading to changes in tibiotalar contact area and increased contact pressures.4,5 Therefore, accurate diagnosis is essential to proper treatment and preventing long-term ankle dysfunction. Ankle arthroscopy is becoming increasingly used for both diagnosis and treatment of syndesmotic injuries. It has been shown to have the highest sensitivity and specificity and often can diagnose injuries previously missed on standard and stress radiographs.6,7 Although parameters for arthroscopic diagnosis have been defined, including disruption of the deep portion of the posterior tibiofibular ligament, rupture of the interosseous ligament with a syndesmotic gap >2 mm, and a chondral fracture of the posterolateral portion of the tibial plafond, these parameters have not been quantified.8 Specifically, the authors were unable to identify
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 33, No 2 (February), 2017: pp 436-444
QUANTIFICATION OF SYNDESMOTIC INSTABILITY Table 1. Demographic Data of Cadavers, Including Age, Sex, and Laterality Specimen 1 2 3 4 5 6 7 8 9 10
Age, yr 48 53 49 63 58 59 59 48 64 52
Sex Male Male Male Male Female Male Female Male Male Male
Laterality Right Left Left Right Right Left Left Left Right Right
literature regarding the different measurements of syndesmotic widening (e.g., 2 mm vs 5 mm of syndesmotic widening) and whether arthroscopic measurement of syndesmotic widening correlates with degree of injury. In addition, the long-term clinical importance of subtle (single-ligamentous) syndesmotic injury is unknown. To begin to understand the clinical relevance of these injuries, it is important to evaluate the ability of arthroscopy to identify subtle syndesmotic injuries as well as its ability to differentiate between sequential levels of injury. Elucidating the degree of injury that arthroscopy is able to detect will likely prevent the over- or undertreatment of syndesmotic injuries. The purpose of this study was to investigate whether arthroscopy or stress radiography can identify instability resulting from single-ligament injury of the ankle syndesmosis and to determine whether either modality is capable of differentiating between various levels of ligament injury.
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standard anteromedial and anterolateral arthroscopic portals were created. An Arthrex ankle arthroscopy distractor strap (AR-1712) was used for noninvasive traction application. A standard force of 18 lb of traction was applied to each specimen, measured using an inline force-measuring spring scale (Fig 1). Each specimen underwent arthroscopic syndesmotic evaluation while intact and after sequential sectioning of the syndesmotic and deltoid ligaments was performed, similar to the model proposed by Stoffel et al.9 The anteroinferior tibiofibular ligament (AITFL), posteroinferior tibiofibular ligament (PITFL), and deltoid ligaments were sharply transected midsubstance under arthroscopic guidance, while the interosseous membrane (IOM) was divided up to 10 cm proximal to the joint line. Open dissection was carried down to the level of each ligament prior to transection. After transection, the skin and subcutaneous tissues were tightly closed. There were 2 groups based on the order of the syndesmotic ligament sectioning. Group 1 (n ¼ 5) consisted of the specimens that were sectioned starting with the AITFL, then sequentially proceeding to the IOM, PITFL, and deltoid, and group 2 (n ¼ 5) consisted of the specimens that were sectioned starting with the deltoid, then proceeding to sequential sectioning of the PITFL, IOM, and AITFL. Arthroscopic measurements were made by placing probes of increasing diameters into the anterolateral portal and inserting them into the space between the tibia and fibula both in the anterior and posterior syndesmosis. The probes used in this study were 2, 2.5, 3, 4, and 5 mm in diameter. Measurements were made by determining the largest probe diameter that could be fit in the distal tibiofibular articulation (Fig 2). Care was taken not to exert an excessive
Methods Ten fresh-frozen unmatched cadaver legs from the midfemur to the toes were included in the present study. Specimens were obtained from the University of Utah School of Medicine Neurobiology and Anatomy Laboratory. The average age of the specimens was 58.3 years. There were 8 male and 2 female legs (5 right, 5 left), and no specimen had any apparent injury to the ankle or syndesmosis based on fluoroscopic imaging. Table 1 contains demographic data including age, sex, and laterality of each cadaver. Each specimen was prepared by removing all of the soft tissues from the femur proximal to the knee, and an intramedullary rod was inserted into the femur to allow for placement into the testing jig. All soft tissue around and distal to the knee was maintained. An arthroscopic examination of the syndesmosis was performed after each step in the sectioning process both with and without noninvasive traction. To perform the arthroscopy, the femur was secured within a stand, and
Fig 1. Testing apparatus: The femur was stripped of proximal soft tissue and attached via a vice grip. Arthroscopy was performed both with and without traction. All soft tissues around and distal to the knee were maintained.
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amount of force while placing the probe into the tibiofibular space. Both the anterior and posterior aspect of the syndesmosis were evaluated for each specimen, with and without traction, after each step in the sectioning process. After each sequential sectioning, external rotation stress radiographs were obtained using fluoroscopy. The tibiofibular overlap (TFO), tibiofibular clear space (TFCS), and medial clear space (MCS) were measured from each radiograph for each step in the sectioning. Generalized estimating equations were used to compare syndesmotic laxity as measured by radiography and maximum probe size as sequential cuts were made. Within-specimen values were treated as having correlated error to account for that nesting of observations. The Holm test was used to adjust individual P values to maintain alpha at 0.05 across the pairwise comparisons of different cuts. In every model, the Gaussian distribution was chosen, making these generalized estimating equations very similar to analysis of variance. Although the detection of systematic, nonrandom, differences in laxity as ligaments are cut validates the impact of making cuts, it has limited clinical application. Therefore, another set of analyses used logistic regression (radiograph) to assess the degree to which the observed laxities could serve as diagnostic of the presence of either of the first ligament cuts.
Results Radiographic Parameter Measurements Tibiofibular Overlap. TFO progressively decreased in groups 1 and 2 from an initial intact baseline average of 4.94 mm (P < .0001, 95% confidence interval [CI] 4.29-5.59) and 4.68 mm (P < .0001, 95% CI 3.465.90), respectively. In group 1, the average TFO decreased to 4.40 mm (P < .0001, 95% CI 3.63-5.17) when the AITFL was transected. This measurement decreased to 2.80 mm when both AITFL and IOM were transected (P < .0001, 95% CI 2.39-3.20), and further to 1.47 mm with AITFL, IOM, and PITFL disruption (P ¼ .04, 95% CI 0.07-2.86). As expected, TFO was less than 0 mm (i.e., syndesmotic diastasis) with all 4 ligaments transected. In group 2, deltoid ligament followed by PITFL, IOM, and AITFL transection resulted in progressively decreasing average TFO values of 3.76 mm (P < .0001, 95% CI 2.97-4.55), 3.02 mm (P < .0001, 95% CI 2.03-4.00), 2.18 mm (P < .0001, 95% CI 1.63-2.73), and less than 0 mm, respectively. Although the change in TFO was not statistically significant when comparing intact to AITFL-transected specimens (P ¼ .29, 95% CI 0.48 to 1.56), the change in TFO was statistically significant when comparing intact to 2-, 3-, and 4-ligament disruption
(P < .0001, 95% CI 1.47-2.81; P ¼ .0004, 95% CI 1.984.97; and P < .0001, 95% CI 4.29-5.59, respectively). TFO was significantly different when comparing single(AITFL) and double-ligament (AITFL, IOM) transection specimens (P ¼ .024, 95% CI 0.58-2.62). Additionally, there was a significant difference when comparing single- and 3- and 4-ligament transection models (P ¼ .0008, 95% CI 1.60-4.26, and P < .0001, 95% CI 3.635.17, respectively). Detection of a statistically significant difference between the TFOs in 2- versus 3-ligament transection specimens was not observed (P ¼ .17, 95% CI 0.23 to 2.90); however, significant differences were found between 2- and 4-ligament disruption models (P < .0001, 95% CI 2.39-3.20). Tibiofibular Clear Space. In group 1, the average baseline measurement for TFCS was 4.72 mm (P < .0001, 95% CI 3.52-5.91). With each sequential ligament sectioning, these values increased to 5.42 mm (AITFL, P < .0001, 95% CI 4.51-6.33), 5.56 mm (AITFL and IOM, P < .0001, 95% CI 4.77-6.35), 7.53 mm (AITFL, IOM, and PITFL, P < .0001, 95% CI 5.89-9.17), and 11.46 mm (AITFL, IOM, PITFL, and deltoid, P < .0001, 95% CI 10.09-12.84). In group 2, the average baseline measurement for TFCS was 5.46 mm (P < .0001, 95% CI 4.95-5.97). With this sequence of transection, there was a less predictable increase in TFCS. With both deltoid transection alone and deltoid and PITFL transection, the TFCS actually decreased to an average of 5.38 mm (P < .0001, 95% CI 4.29-6.46) and 5.34 mm (P < .0001, 95% CI 4.25-6.43), respectively. With higher degrees of ligament involvement (i.e., deltoid, PITFL, and IOM, and all 4 ligaments transected), the TFCS increased to 6.08 mm (P < .0001, 95% CI 4.83-7.33) and 11.10 mm (P < .0001, 95% CI 9.2612.94), respectively. Although there was a statistically significant difference in TFCS between intact and single-ligament (AITFL) disruption specimens (P ¼ .0076, 95% CI 0.29-1.11), it approached but did not reach statistical significance comparing intact to double- or tripleligament disruption specimens (P ¼ .067, 95% CI 1.70 to 0.18, P ¼ .067, 95% CI 5.05 to 0.57). There was a statistically significant difference in TFCS when comparing intact to complete ligament transection models (P < .0001, 95% CI 4.66-8.82). Statistical significance was reached for 2-ligament versus complete transection specimens (P < .0001, 95% CI 4.467.34) but not for 2- versus 3-ligament disruption models (P ¼ .09, 95% CI 3.83 to 0.11). Medial Clear Space. The average MCS for groups 1 and 2 was 4.00 mm (P < .0001, 95% CI 3.13-4.87) and 4.78 mm (P < .0001, 95% CI 3.91-5.65), respectively. In group 1, progressive ligament transection beginning with the AITFL resulted in MCS measurements of 3.96 mm
QUANTIFICATION OF SYNDESMOTIC INSTABILITY
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Fig 2. (A) Syndesmosis intact and 2-mm probe unable to fit in the anterior syndesmosis. (B) AITFL transected, 2.5-mm probe within the syndesmosis. (C) AITFL and IOM transected, 3-mm probe able to fit within the syndesmosis. (D) AITFL, IOM, and PITFL transected, 5-mm probe within syndesmosis. (E) AITFL, IOM, PITFL, and deltoid transected, with 5-mm probe in the syndesmosis. (AITFL, anteroinferior tibiofibular ligament; IOM, interosseous membrane; PITFL, posteroinferior tibiofibular ligament.)
(AITFL, P < .0001, 95% CI 3.28-4.64), 5.04 mm (AITFL and IOM, P < .0001, 95% CI 3.93-6.15), 5.73 mm (AITFL, IOM, and PITFL, P < .0001, 95% CI 4.49-6.98), and 9.82 mm (P < .0001, 95% CI 8.11-11.53) with all 4 syndesmotic ligaments disrupted. Group 2 corresponding values were the following: 4.92 mm (P < .0001, 95% CI 4.17-5.67), 5.64 mm (P < .0001, 95% CI 5.02-6.27), 5.76 mm (P < .0001, 95% CI 4.74-6.78), and 10.28 mm (P < .0001, 95% CI 7.34-13.20). MCS approached but was unable to detect statistically significant differences between intact and single/ double-ligament transection (P ¼ .82, 95% CI 0.32 to 0.40, and P ¼ .10, 95% CI 2.02 to 0.04, respectively). MCS was able to distinguish statistically significant differences between intact and 3- and 4-ligament transections (P ¼ .006, 95% CI 0.75-2.70, and P < .0001, 95% CI 4.12-7.52). The difference in MCS approached but did not reach significance with regards to single- (AITFL) and double-ligament (AITFL, IOM) disruption models (P ¼ .06, 95% CI 1.96 to 0.20). It did, however, reach significance with regard to distinguishing single- versus 3- and 4-ligament transection specimens (P ¼ .0009, 95% CI 0.93-2.62, and P < .0001, 95% CI 4.33-7.39, respectively). Similarly, MCS measurements approached but did not reach statistical significance in distinguishing 2versus 3-ligament transection (P ¼ .06, 95% CI 0.15
to 1.23); however, MCS reached significance in differentiating specimens with 2 versus 4 ligaments transected (P < .0001, 95% CI 3.70-5.86). Arthroscopic Measurements Although measurements were obtained in specimens with and without traction, the results obtained in these 2 samples were not significantly different. Therefore, only the data from the group without traction was used for final analysis. Anterior Probing In specimens with an intact syndesmosis, the average probe size able to be placed into the anterior syndesmosis was 0.90 mm (P ¼ .04, 95% CI 0.06-1.74) in group 1 and 0.80 mm (P ¼ .0001, 95% CI 0.44-1.17) in group 2. In group 1, this value increased with sequential ligament transection to 3.00 mm (AITFL, P < .0001, 95% CI 2.25-3.75), 3.80 mm (AITFL and IOM, P ¼ .05, 95% CI 3.06-4.54), 5.00 mm (AITFL, IOM, and PITFL, P < .0001), and 5.00 mm (AITFL, IOM, PITFL, and deltoid, P < .0001). In group 2, the corresponding values were 1.60 mm (deltoid, P ¼ .001, 95% CI 0.672.53), 2.00 mm (deltoid and PITFL, P ¼ .004, 95% CI 0.71-3.29), 2.30 mm (deltoid, PITFL, and IOM, P ¼ .002, 95% CI 0.89-3.70), and 4.90 mm with complete ligament transection (P ¼ .0004, 95% CI 4.71-5.08).
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Table 2. Parameter Measurements During Each Stage of Transection in Group 1 and Group 2 Group 1 Parameter TFO TFCS MCS AP PP
4.94 4.72 4.00 0.90 2.65
Intact (4.29-5.59) (3.52-5.91) (3.13-4.87) (0.06-1.74) (2.01-3.29)
þAITFL 4.40 (3.46-5.90) 5.42 (4.51-6.33) 3.96 (3.28-4.64) 3.00 (2.25-3.75) 3.60 (2.93-4.27)
2.80 5.56 5.04 3.80 4.40
þIOM (2.39-3.20) (4.77-6.35) (3.93-6.15) (3.06-4.54) (3.95-4.85)
1.47 7.53 5.73 5.00 5.00
þPITFL (0.07-2.86) (5.89-9.17) (4.49-6.98) (NA) (NA)
<0 11.46 9.82 5.00 5.00
þDeltoid (NA) (10.09-12.84) (8.11-11.53) (NA) (NA)
Group 2 Parameter TFO TFCS MCS AP PP
Intact 4.68 5.46 4.78 0.80 2.15
(3.46-5.90) (4.95-5.97) (3.91-5.65) (0.44-1.17) (1.78-2.52)
þDeltoid 3.76 5.38 4.92 1.60 3.40
(2.97-4.55) (4.29-6.46) (4.17-5.67) (0.67-2.53) (2.61-4.12)
þPITFL 3.02 5.34 5.64 2.00 3.90
(2.03-4.00) (4.25-6.43) (5.02-6.27) (0.71-3.29) (3.20-4.63)
þIOM 2.18 6.08 5.76 2.30 4.30
(1.63-2.73) (4.83-7.33) (4.74-6.78) (0.89-3.70) (3.83-4.77)
þAITFL <0 11.10 10.28 4.90 4.90
(NA) (9.26-12.94) (7.34-13.20) (4.71-5.08) (4.71-5.08)
NOTE. All values are in millimeters, with 95% confidence intervals included in parentheses. Group 1 transection sequence: AITFL, IOM, PITFL, deltoid. Group 2 transection sequence: deltoid, PITFL, IOM, AITFL. AITFL, anteroinferior tibiofibular ligament; AP, anterior probe size; IOM, interosseous membrane; MCS, medial clear space; NA, not applicable; PITFL, posteroinferior tibiofibular ligament; PP, posterior probe size; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.
Anterior probe size (AP) reached statistical significance with regards to distinguishing between intact and AITFL transected specimens (P < .0001, 95% CI 1.59-2.61). AP was able to detect statistically significant differences comparing single-ligament (AITFL) with 2- (AITFL and IOM), 3- (AITFL, IOM, and PITFL), and 4-ligament (AITFL, IOM, PITFL, and deltoid) disruptions (P ¼ .0072, <.0001, and <.0001, 95% CIs 0.23-1.37, 1.25-2.75, and 0.93-2.75, respectively). In addition, statistically significant differences were observed between 2- and 3-ligament (P ¼ .002, 95% CI 0.46-1.94), as well as 2- and 4-ligament (P ¼ .02, 95% CI 0.46-1.94) transections but not between 3- and 4-ligament disruption models (P > .99). Posterior Probing In specimens with an intact syndesmosis, the average probe size able to be placed into the posterior syndesmosis was 2.65 mm (P < .0001, 95% CI 2.01-3.29) in group 1 and 2.15 mm (P < .0001, 95% CI 1.78-2.52) in group 2. In group 1, this value increased with sequential ligament transection to 3.60 mm (AITFL) (P < .0001, 95% CI 2.934.27), 4.40 mm (AITFL, IOM) (P < .0001, 95% CI 3.954.85), 5.00 mm (AITFL, IOM, PITFL) (P < .0001) and 5.00 mm (AITFL, IOM, PITFL, deltoid) (P < .0001). In group 2, the corresponding values were 3.40 mm (deltoid) (P < .0001, 95% CI 2.61-4.12), 3.90 mm (deltoid, PITFL) (P < .0001, 95% CI 3.20-4.63), 4.30 mm (deltoid, PITFL, IOM) (P < .0001, 95% CI 3.83-4.77) and 4.90 mm (deltoid, PITFL, IOM, and AITFL) (P < .0001, 95% CI 4.71-5.08). Posterior probe size, much like anterior probe size, was effective at detecting statistically significant
differences between intact and single-, double-, triple-, and complete ligament transections (P values .0006, <.0001, <.0001, and <.001, 95% CIs 0.53-1.37, 1.292.20, 1.71-2.99, and 1.71-2.99, respectively). Posterior probing also found statistically significant differences in probe size between single- and double-, triple-, and complete ligament transection models (P values .0075, .0010, and .0010, 95% CIs 0.33-1.27, 0.73-2.07, and 0.73-2.07, respectively). In addition, posterior probing was able to distinguish between 2- and 3-ligament (P ¼ .03, 95% CI 0.15-1.05) and 2- and 4-ligament (P ¼ .03, 95% CI 0.15-1.05) transections. Posterior probe size did not find significant differences between 3- and 4-ligament disruption models (P > .99). A summary of the radiographic and arthroscopic testing is shown in Tables 2 and 3, respectively, as well as Figures 3 and 4.
Discussion This study reveals that arthroscopy is capable of detecting differences in syndesmotic diastasis resulting from sequential ligament disruption. Although stress fluoroscopy is the most commonly used dynamic diagnostic modality, including intraoperatively, it has been shown to be inferior and unreliable in comparison. For example, TFO and MCS were unable to detect significant differences between intact and AITFLtransected specimens. And although TFCS was shown to be able to identify significant differences between intact and AITFL disruption, it was unable to detect significant differences between intact and 2/3-ligament disruption models. Arthroscopy was universally more reliable, especially in detecting subtle injuries, with
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QUANTIFICATION OF SYNDESMOTIC INSTABILITY Table 3. Individual Parameter’s Ability to Distinguish Between Various Levels of Ligament Transection in Group 1 Intact A. TFO Intact Single Double Triple Complete B. TFCS Intact Single Double Triple Complete C. MCS Intact Single Double Triple Complete D. AP Intact Single Double Triple Complete E. PP Intact Single Double Triple Complete
e e e e e e e e e e e e e e e
Single P ¼ .29 (0.48 to 1.56) e e e e P ¼ .0076 (0.29-1.11) e e e e P ¼ .82 (0.32 to 0.40) e e e e
Double P < .0001 (1.47-2.81) P ¼ .024 (0.58-2.62) e e e
Triple
Complete
P ¼ .0004 (1.98-4.97) P ¼ .0008 (1.60-4.26) P ¼ .17 (0.23 to 2.90) e e
P < .0001 (4.29-5.59) P < .0001 (3.63-5.17) P < .0001 (2.39-3.20) P ¼ .13 (0.07 to 2.86) e
P ¼ .067 (0.18 to 1.70) P ¼ .56 (0.63 to 0.36) e e e
P ¼ .067 (0.57 to 5.05) P ¼ .058 (0.07 to 4.31) P ¼ .09 (0.11 to 3.83) e e
P P P P
< < < <
.0001 .0001 .0001 .0001
(4.66-8.82) (4.15-7.93) (4.46-7.34) (2.59-5.27) e
P ¼ .10 (2.02 to 0.04) P ¼ .06 (1.96 to 0.20) e e e
P ¼ .006 (0.75-2.70) P ¼ .0009 (0.93 to 2.62) P ¼ .06 (0.15 to 1.23) e e
P P P P
< < < <
.0001 .0001 .0001 .0001
(4.12-7.52) (4.33-7.39) (3.70-5.86) (3.30-4.87) e
e e e e e
P < .0001 (1.59-2.61) e e e e
P < .0001 (2.37-3.43) P ¼ .0072 (0.23-1.37) e e e
P < .0001 (3.26-4.94) P < .0001 (1.25-2.75) P ¼ .002 (0.46-1.94) e e
P < .0001 (3.26-4.93) P < .0001 (0.93-2.75) P ¼ .02 (0.46-1.94) P > .99 e
e e e e e
P ¼ .0006 (0.53-1.37) e e e e
P < .0001 (1.29-2.20) P ¼ .0075 (0.33-1.27) e e e
P < .0001 (1.71-2.99) P ¼ .001 (0.73-2.07) P ¼ .03 (0.15-1.05) e e
P < .0001 (1.71-2.99) P ¼ .001 (0.73-2.07) P ¼ .03 (0.15-1.05) P > .99 e
NOTE. Single ¼ AITFL; Double ¼ AITFL/IOM; Triple ¼ AITFL/IOM/PITFL; Complete ¼ AITFL/IOM/PITFL/deltoid. Values within parentheses are 95% confidence intervals. Group 1 was chosen for presentation as this sequence represents a clinical mechanism of injury (supinationexternal rotation). Of the radiographic parameters, only TFCS was able to distinguish between intact and AITFL-transected specimens; however, TFCS did not reveal significance between intact and double- or triple-ligament transection. Arthroscopic probing was universally better at distinguishing between sequential levels of ligament injury and was only unable to distinguish between 3- and complete ligament transection models. AITFL, anteroinferior tibiofibular ligament; AP, anterior probe size; IOM, interosseous membrane; MCS, medial clear space; PITFL, posteroinferior tibiofibular ligament; PP, posterior probe size; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.
Fig 3. Group 1. There was minimal difference in radiographic measurements obtained after 1 ligament was transected whereas the difference was significant between intact and AITFL sectioned specimens using arthroscopy. Radiographs were clearly influenced by successive syndesmotic disruption but stress views were not able to distinguish between intact and single-ligament disruption. Asterisks represent statistically significant measurements (P < .05). (AITFL, anteroinferior tibiofibular ligament; IOM, interosseous membrane; MCS, medial clear space; PITFL, posteroinferior tibiofibular ligament; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.)
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Fig 4. Group 2. Similarly, in group 2, arthroscopy could identify statistically significant differences between intact and deltoidtransected specimens, and between sequential ligamentous transection. Radiographs could not identify a significant difference until at least 3 ligaments had been transected. Asterisks indicate statistically significant measurements (P < .05). (IOM, interosseous membrane; MCS, medial clear space; PITFL, posteroinferior tibiofibular ligament; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.)
both anterior and posterior probing being able to distinguish between intact and AITFL-transected specimens. In addition, arthroscopy is able to distinguish between most sequential injury patterns, that is, intact versus single-ligament, single- versus double-ligament, and double- versus triple-ligament transections. Only 3- and 4-ligament disruption models were unable to be distinguished with arthroscopic probing. Syndesmotic injury is a broad term with significant variability in the extent of soft tissue and ligamentous involvement, associated fracture and resulting ankle instability. Historically, optimal indications for treatment of these injuries has been difficult to determine because of an incomplete understanding of the clinical implications associated with varying degrees of ligamentous damage. The authors found no study that has used arthroscopy to quantify the amount of instability resulting from injury to single ligaments such as the AITFL or deltoid, or whether arthroscopy is capable of detecting differences in syndesmotic widening between different injury patterns. This information is important from both a research and clinical perspective, as each individual ligament does not contribute equally to the stability of the ankle mortise. Thus, “syndesmotic injury” as a broad term should be thought of according to changes in stability resulting from various combinations of ligament involvement. One must also make the distinction between ligament injury and syndesmotic instability. In a cadaveric study by Ogilvie-Harris et al., the contribution of each syndesmotic ligament to ankle stability was calculated. The authors found that the AITFL, IOM, and PITFL provided 35%, 22%, and 42% of total ankle stability, respectively.10 Although the PITFL contributes
nearly half of the resistance to syndesmotic diastasis, isolated injuries to the PITFL are rare. A study by Oae et al. evaluated magnetic resonance imaging (MRI) for diagnosis of syndesmotic injuries and found that only 5 of 28 patients with a syndesmotic injury had a PITFL injury, and no patient had an isolated PITFL injury. On the other hand, all patients with a syndesmotic injury had an AITFL injury.11 Similarly, a study by Takao et al.7 revealed that all patients diagnosed with syndesmotic injury by arthroscopic means had injury to the AITFL, whereas less than 50% had PITFL injury and no patients were found to have an isolated PITFL injury. Thus, it is possible that injury to the AITFL in isolation or in combination with IOM injury may produce subtle yet clinically relevant instability previously missed by clinical exam and stress radiography. Making the diagnosis of syndesmotic instability can be challenging and yet is critically important for providing adequate treatment for patients. It has been shown that clinical examination findings, preoperative stress radiographs, and intraoperative fluoroscopy are insufficient in identifying all syndesmotic injuries.3,6,12-16 The literature regarding the utility of MRI in the diagnosis of syndesmotic injury is promising, with nearly 100% sensitivity across all studies.17,18 However, there is potential for false positive results, and MRI provides a static image of instability, a process that is dynamic in nature.19 Therefore, arthroscopy has been introduced as both a possible diagnostic and therapeutic tool when dealing with these injuries. In this study, stress fluoroscopy was generally worse than arthroscopy at identifying changes in syndesmotic diastasis between various levels of ligamentous involvement, particularly when only 1 or 2 ligaments were transected. Use of
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stress radiography/fluoroscopy as the sole means of determining syndesmotic stability may lead to missing a significant number of lower-grade injuries involving, for example, only the AITFL or AITFL/IOM. The clinical and prognostic implications of varying degrees of syndesmotic ligament involvement are also poorly understood, although with the increasing use of arthroscopy and MRI it is now possible to evaluate subtle syndesmotic injuries that may have previously been overlooked in the setting of acute and chronic injury.20 Beginning to study these modalities to quantify the extent of damage and resulting instability is paramount in the process of developing objective methods for arthroscopic evaluation of the syndesmosis. In 2001, Takao et al. presented data on the ability of radiography (AP and mortise) and arthroscopy to detect syndesmotic diastasis in 38 Weber B ankle fractures. Although arthroscopy was able to detect injury in 87% of patients, AP and mortise radiographs identified syndesmotic injury in only 42% and 55%, respectively.16 In 2003, the same group was able to report on the improved diagnostic accuracy of arthroscopy, with 100% of syndesmotic injuries detected versus 63% with standard radiography.7 Liu and colleagues further explored the capability of arthroscopic evaluation of the syndesmosis in 2005 by comparing intraoperative stress radiography and arthroscopy in 53 Weber B and C ankle fractures. This was the first study to report instability in multiple planes (coronal, sagittal, and rotational). Stress views identified 16 cases of diastasis, whereas arthroscopy was able to identify an additional 19 cases using 2 mm of translation in any plane as a threshold for instability. All syndesmotic injuries were treated with screw fixation and subsequent removal at 12 weeks. Arthroscopy was repeated at the time of screw removal, and syndesmotic ligament healing was observed in all cases and no further evidence of instability was noted. However, the authors comment that there is a continued role for intraoperative stress radiography, as arthroscopy is incapable of assessing complex fibular “fracture reduction and proper restoration of fibular length and longitudinal orientation of the syndesmosis.”6 In a recent study by Watson and colleagues, arthroscopic evaluation of cadaveric below-knee specimens was able to detect multiplanar syndesmotic instability in the transverse, sagittal, and coronal planes by applying increasing forces and measuring the amount of fibular displacement that resulted. Four ligament disruption models were chosen for analysis: intact, AITFL/IOM, AITFL/IOM/ATFL/CFL, and AITFL/IOM/ATFL/CFL/ PITFL/TL disruption.21 The ligament transection model used for the current study differs from the aforementioned analysis in several regards. The basis for this model is predicated by the work of Stoffel and
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colleagues,15 with 2 groups representing transection in reverse directions beginning with either the AITFL (group 1) or deltoid ligament (group 2). We did not perform ATFL/CFL transection, as these lateral ligaments are not considered primary restraints to syndesmotic diastasis and typically are not involved when injury to the syndesmotic ligamentous complex is present.22 In addition, solitary AITFL transection was performed to evaluate whether injury to this ligament results in instability, and to determine if this can be appreciated arthroscopically. Deltoid ligament disruption was included for 2 reasons. This ligament is often injured in conjunction with mechanisms leading to syndesmosis injury (e.g., SER4 deltoid). Furthermore, repair in the setting of bimalleolar equivalent ankle fracture has been shown to confer stability comparable to syndesmotic screw fixation, indicating that the deltoid may have a role in providing restraint to syndesmotic diastasis.1 Finally, cadaveric above-knee amputation specimens were used, as this maintained the integrity of the IOM and the gastrocsoleus complex. We also chose to transect the ligaments in 2 groups in different order to decrease the possibility that repetitive measurements could increase the syndesmotic diastasis inadvertently. The current study performed arthroscopic examinations both with and without traction, and found no significant differences in final measurements between the 2 groups. Therefore, only the data regarding arthroscopic probe examination without traction was used for final analysis. However, it is important to note that consistency in the use or avoidance traction during syndesmotic probing should be maintained so the examiner has a reproducible baseline for the syndesmotic appearance. Limitations There are several limitations to the current study. Cadaver specimens and a small sample size were used for the study. No power analysis was performed prior to beginning the study, thus making the potential for insufficient power a possibility. Only the major ligamentous contributors to the syndesmosis were studied; it is possible that there are additional minor soft tissue restraints such as the ATFL and CFL that may contribute to overall stability. Investigators were not blinded to the level of ligament injury, adding a potential for observation bias. Finally, although each ankle was examined for evidence of chronic injury and arthritic changes, there were no available data regarding prior ankle injury and subsequent treatment.
Conclusions Stress radiography did not distinguish between intact and single-ligament disruption and were unreliable in distinguishing between sequential transection models.
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Arthroscopy significantly predicted isolated disruption of the AITFL or deltoid ligaments. Also, probing was able to differentiate between most patterns of ligament injury, including sequential transections.
References 1. Hopkinson WJ, St Pierre P, Ryan JB, Wheeler JH. Syndesmosis sprains of the ankle. Foot Ankle 1990;10: 325-330. 2. Lauge-Hansen N. Fractures of the ankle. II. Combined experimental-surgical and experimental-roentgenologic investigations. Arch Surg 1950;60:957-985. 3. Zalavras C, Thordarson D. Ankle syndesmotic injury. J Am Acad Orthop Surg 2007;15:330-339. 4. Burns WC, Prakash K, Adelaar R, Beaudoin A, Krause W. Tibiotalar joint dynamics: indications for the syndesmotic screwdA cadaver study. Foot Ankle 1993;14:153-158. 5. Ramsey PL, Hamilton W. Changes in tibiotalar area of contact caused by lateral talar shift. J Bone Joint Surg Am 1976;58:356-357. 6. Lui TH, Ip K, Chow HT. Comparison of radiologic and arthroscopic diagnoses of distal tibiofibular syndesmosis disruption in acute ankle fracture. Arthroscopy 2005;21: 1370. 7. Takao M, Ochi M, Oae K, Naito K, Uchio Y. Diagnosis of a tear of the tibiofibular syndesmosis. The role of arthroscopy of the ankle. J Bone Joint Surg Br 2003;85:324-329. 8. Ogilvie-Harris DJ, Reed SC. Disruption of the ankle syndesmosis: Diagnosis and treatment by arthroscopic surgery. Arthroscopy 1994;10:561-568. 9. Stoffel K, Wysocki D, Baddour E, Nicholls R, Yates P. Comparison of two intraoperative assessment methods for injuries to the ankle syndesmosis. A cadaveric study. J Bone Joint Surg Am 2009;91:2646-2652. 10. Ogilvie-Harris DJ, Reed SC, Hedman TP. Disruption of the ankle syndesmosis: Biomechanical study of the ligamentous restraints. Arthroscopy 1994;10:558-560. 11. Oae K, Takao M, Naito K, et al. Injury of the tibiofibular syndesmosis: Value of MR imaging for diagnosis. Radiology 2003;227:155-161.
12. Sman AD, Hiller CE, Refshauge KM. Diagnostic accuracy of clinical tests for diagnosis of ankle syndesmosis injury: A systematic review. Br J Sports Med 2013;47:620-628. 13. Beumer A, van Hemert WLW, Niesing R, et al. Radiographic measurement of the distal tibiofibular syndesmosis has limited use. Clin Orthop Relat Res 2004;423: 227-234. 14. Pneumaticos SG, Noble PC, Chatziioannou SN, Trevino SG. The effects of rotation on radiographic evaluation of the tibiofibular syndesmosis. Foot Ankle Int 2002;23:107-111. 15. Nielson JH, Gardner MJ, Peterson MGE, et al. Radiographic measurements do not predict syndesmotic injury in ankle fractures: An MRI study. Clin Orthop Relat Res 2005;436:216-221. 16. Takao M, Ochi M, Naito K, et al. Arthroscopic diagnosis of tibiofibular syndesmosis disruption. Arthroscopy 2001;17: 836-843. 17. Roemer FW, Jomaah N, Niu J, et al. Ligamentous injuries and the risk of associated tissue damage in acute ankle sprains in athletes: A cross-sectional MRI study. Am J Sports Med 2014;42:1549-1557. 18. Vogl TJ, Hochmuth K, Diebold T, et al. Magnetic resonance imaging in the diagnosis of acute injured distal tibiofibular syndesmosis. Invest Radiol 1997;32:401-409. 19. Ebraheim NA, Lu J, Yang H, Mekhail AO, Yeasting RA. Radiographic and CT evaluation of tibiofibular syndesmotic diastasis: A cadaver study. Foot Ankle Int 1997;18:693-698. 20. Clanton TO, Ho CP, Williams BT, et al. Magnetic resonance imaging characterization of individual ankle syndesmosis structures in asymptomatic and surgically treated cohorts. Knee Surg Sports Traumatol Arthrosc 2016;24:2089-2102. 21. Watson BC, Lucas DE, Simpson GA, Berlet GC, Hyer CF. Arthroscopic evaluation of syndesmotic instability in a cadaveric model. Foot Ankle Int 2015;36:1362-1368. 22. Uys HD, Rijke AM. Clinical association of acute lateral ankle sprain with syndesmotic involvement: A stress radiography and magnetic resonance imaging study. Am J Sports Med 2002;30:816-822.
Purpose: To investigate whether arthroscopy or stress radiography can identify instability resulting from single-ligament injury of the ankle syndesmosis and to determine whether either modality is capable of differentiating between various levels of ligament injury. Methods: Syndesmotic/deltoid ligament sectioning was performed in 10 cadaver legs. Arthroscopic evaluation and fluoroscopic stress testing were completed after each sectioning. In group 1 (n ¼ 5), sectioning began with anteroinferior tibiofibular ligament (AITFL), then interosseous membrane (IOM), posteroinferior tibiofibular ligament (PITFL), and deltoid. In group 2 (n ¼ 5), this order was reversed. Measurements were made by determining the largest-sized probe that would fit in the anterior and posterior syndesmosis. Radiographic parameters included tibiofibular overlap/clear space and medial clear space. Results: No radiographic measurement proved useful in distinguishing between intact and transected AITFL. Anterior probe (AP) size reached significance when distinguishing between intact and AITFL-transected specimens (P < .0001). AP detected significant differences comparing single with 2-, 3-, and 4-ligament (AITFL, IOM, PITFL, deltoid) disruptions (P ¼ .05, <.0001, and <.0001, respectively). Significant differences were observed between 2- and 3/4-ligament (P ¼ .02) transections. Posterior probe (PP) size detected significant differences between intact and single-, double-, triple-, and complete ligament transections (P values .0006, <.0001, <.0001, <.001, respectively). PP detected significant differences between single- and double-, triple-, and complete ligament transection models (P ¼ .0075, .0010, and .0010, respectively). PP distinguished between 2- and 3/4ligament (P ¼ .03) transections. Conclusions: Stress radiography did not distinguish between intact and single-ligament disruption, and was unreliable in distinguishing between sequential transection models. Arthroscopy significantly predicted isolated disruption of the AITFL or deltoid ligaments. Also, probing was able to differentiate between most patterns of ligament injury, including sequential transections. Clinical Relevance: These data can aid surgeons during arthroscopy of the ankle when attempting to correlate intraoperative syndesmotic evaluation findings with the extent of ligament injury.
I
njury to the syndesmosis is common and occurs in up to 11% of all ankle injuries.1 These injuries can be purely ligamentous or may be associated with fractures,
From the Department of Orthopaedic Surgery, The Warren Alpert School of Medicine at Brown University, Rhode Island Hospital (R.F., T.B., A.J.F., J.T.M., B.B.), Providence, Rhode Island; Capital Orthopedic and Sports Medicine (R.B.K.), Flowood, Mississippi; and Department of Orthopaedics, University of Utah (F.N.), Salt Lake City, Utah, U.S.A. The authors report the following potential conflicts of interest or sources of funding: F.N. receives consultancy fees and royalties from Smith & Nephew and has stock/stock options in Connextions, First Ray, Surgical Frontiers, and Mortise Medical. Received October 26, 2015; accepted November 3, 2016. Address correspondence to Amanda J. Fantry, M.D., The Warren Alpert School of Medicine at Brown University, Rhode Island Hospital, 593 Eddy Street, Providence, RI 02903, U.S.A. E-mail: [email protected] Ó 2016 by the Arthroscopy Association of North America 0749-8063/15986/$36.00 http://dx.doi.org/10.1016/j.arthro.2016.11.008
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and they can be categorized by the Lauge-Hansen classification system.2,3 Injury to the syndesmotic ligaments may cause instability of the ankle, leading to changes in tibiotalar contact area and increased contact pressures.4,5 Therefore, accurate diagnosis is essential to proper treatment and preventing long-term ankle dysfunction. Ankle arthroscopy is becoming increasingly used for both diagnosis and treatment of syndesmotic injuries. It has been shown to have the highest sensitivity and specificity and often can diagnose injuries previously missed on standard and stress radiographs.6,7 Although parameters for arthroscopic diagnosis have been defined, including disruption of the deep portion of the posterior tibiofibular ligament, rupture of the interosseous ligament with a syndesmotic gap >2 mm, and a chondral fracture of the posterolateral portion of the tibial plafond, these parameters have not been quantified.8 Specifically, the authors were unable to identify
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 33, No 2 (February), 2017: pp 436-444
QUANTIFICATION OF SYNDESMOTIC INSTABILITY Table 1. Demographic Data of Cadavers, Including Age, Sex, and Laterality Specimen 1 2 3 4 5 6 7 8 9 10
Age, yr 48 53 49 63 58 59 59 48 64 52
Sex Male Male Male Male Female Male Female Male Male Male
Laterality Right Left Left Right Right Left Left Left Right Right
literature regarding the different measurements of syndesmotic widening (e.g., 2 mm vs 5 mm of syndesmotic widening) and whether arthroscopic measurement of syndesmotic widening correlates with degree of injury. In addition, the long-term clinical importance of subtle (single-ligamentous) syndesmotic injury is unknown. To begin to understand the clinical relevance of these injuries, it is important to evaluate the ability of arthroscopy to identify subtle syndesmotic injuries as well as its ability to differentiate between sequential levels of injury. Elucidating the degree of injury that arthroscopy is able to detect will likely prevent the over- or undertreatment of syndesmotic injuries. The purpose of this study was to investigate whether arthroscopy or stress radiography can identify instability resulting from single-ligament injury of the ankle syndesmosis and to determine whether either modality is capable of differentiating between various levels of ligament injury.
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standard anteromedial and anterolateral arthroscopic portals were created. An Arthrex ankle arthroscopy distractor strap (AR-1712) was used for noninvasive traction application. A standard force of 18 lb of traction was applied to each specimen, measured using an inline force-measuring spring scale (Fig 1). Each specimen underwent arthroscopic syndesmotic evaluation while intact and after sequential sectioning of the syndesmotic and deltoid ligaments was performed, similar to the model proposed by Stoffel et al.9 The anteroinferior tibiofibular ligament (AITFL), posteroinferior tibiofibular ligament (PITFL), and deltoid ligaments were sharply transected midsubstance under arthroscopic guidance, while the interosseous membrane (IOM) was divided up to 10 cm proximal to the joint line. Open dissection was carried down to the level of each ligament prior to transection. After transection, the skin and subcutaneous tissues were tightly closed. There were 2 groups based on the order of the syndesmotic ligament sectioning. Group 1 (n ¼ 5) consisted of the specimens that were sectioned starting with the AITFL, then sequentially proceeding to the IOM, PITFL, and deltoid, and group 2 (n ¼ 5) consisted of the specimens that were sectioned starting with the deltoid, then proceeding to sequential sectioning of the PITFL, IOM, and AITFL. Arthroscopic measurements were made by placing probes of increasing diameters into the anterolateral portal and inserting them into the space between the tibia and fibula both in the anterior and posterior syndesmosis. The probes used in this study were 2, 2.5, 3, 4, and 5 mm in diameter. Measurements were made by determining the largest probe diameter that could be fit in the distal tibiofibular articulation (Fig 2). Care was taken not to exert an excessive
Methods Ten fresh-frozen unmatched cadaver legs from the midfemur to the toes were included in the present study. Specimens were obtained from the University of Utah School of Medicine Neurobiology and Anatomy Laboratory. The average age of the specimens was 58.3 years. There were 8 male and 2 female legs (5 right, 5 left), and no specimen had any apparent injury to the ankle or syndesmosis based on fluoroscopic imaging. Table 1 contains demographic data including age, sex, and laterality of each cadaver. Each specimen was prepared by removing all of the soft tissues from the femur proximal to the knee, and an intramedullary rod was inserted into the femur to allow for placement into the testing jig. All soft tissue around and distal to the knee was maintained. An arthroscopic examination of the syndesmosis was performed after each step in the sectioning process both with and without noninvasive traction. To perform the arthroscopy, the femur was secured within a stand, and
Fig 1. Testing apparatus: The femur was stripped of proximal soft tissue and attached via a vice grip. Arthroscopy was performed both with and without traction. All soft tissues around and distal to the knee were maintained.
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amount of force while placing the probe into the tibiofibular space. Both the anterior and posterior aspect of the syndesmosis were evaluated for each specimen, with and without traction, after each step in the sectioning process. After each sequential sectioning, external rotation stress radiographs were obtained using fluoroscopy. The tibiofibular overlap (TFO), tibiofibular clear space (TFCS), and medial clear space (MCS) were measured from each radiograph for each step in the sectioning. Generalized estimating equations were used to compare syndesmotic laxity as measured by radiography and maximum probe size as sequential cuts were made. Within-specimen values were treated as having correlated error to account for that nesting of observations. The Holm test was used to adjust individual P values to maintain alpha at 0.05 across the pairwise comparisons of different cuts. In every model, the Gaussian distribution was chosen, making these generalized estimating equations very similar to analysis of variance. Although the detection of systematic, nonrandom, differences in laxity as ligaments are cut validates the impact of making cuts, it has limited clinical application. Therefore, another set of analyses used logistic regression (radiograph) to assess the degree to which the observed laxities could serve as diagnostic of the presence of either of the first ligament cuts.
Results Radiographic Parameter Measurements Tibiofibular Overlap. TFO progressively decreased in groups 1 and 2 from an initial intact baseline average of 4.94 mm (P < .0001, 95% confidence interval [CI] 4.29-5.59) and 4.68 mm (P < .0001, 95% CI 3.465.90), respectively. In group 1, the average TFO decreased to 4.40 mm (P < .0001, 95% CI 3.63-5.17) when the AITFL was transected. This measurement decreased to 2.80 mm when both AITFL and IOM were transected (P < .0001, 95% CI 2.39-3.20), and further to 1.47 mm with AITFL, IOM, and PITFL disruption (P ¼ .04, 95% CI 0.07-2.86). As expected, TFO was less than 0 mm (i.e., syndesmotic diastasis) with all 4 ligaments transected. In group 2, deltoid ligament followed by PITFL, IOM, and AITFL transection resulted in progressively decreasing average TFO values of 3.76 mm (P < .0001, 95% CI 2.97-4.55), 3.02 mm (P < .0001, 95% CI 2.03-4.00), 2.18 mm (P < .0001, 95% CI 1.63-2.73), and less than 0 mm, respectively. Although the change in TFO was not statistically significant when comparing intact to AITFL-transected specimens (P ¼ .29, 95% CI 0.48 to 1.56), the change in TFO was statistically significant when comparing intact to 2-, 3-, and 4-ligament disruption
(P < .0001, 95% CI 1.47-2.81; P ¼ .0004, 95% CI 1.984.97; and P < .0001, 95% CI 4.29-5.59, respectively). TFO was significantly different when comparing single(AITFL) and double-ligament (AITFL, IOM) transection specimens (P ¼ .024, 95% CI 0.58-2.62). Additionally, there was a significant difference when comparing single- and 3- and 4-ligament transection models (P ¼ .0008, 95% CI 1.60-4.26, and P < .0001, 95% CI 3.635.17, respectively). Detection of a statistically significant difference between the TFOs in 2- versus 3-ligament transection specimens was not observed (P ¼ .17, 95% CI 0.23 to 2.90); however, significant differences were found between 2- and 4-ligament disruption models (P < .0001, 95% CI 2.39-3.20). Tibiofibular Clear Space. In group 1, the average baseline measurement for TFCS was 4.72 mm (P < .0001, 95% CI 3.52-5.91). With each sequential ligament sectioning, these values increased to 5.42 mm (AITFL, P < .0001, 95% CI 4.51-6.33), 5.56 mm (AITFL and IOM, P < .0001, 95% CI 4.77-6.35), 7.53 mm (AITFL, IOM, and PITFL, P < .0001, 95% CI 5.89-9.17), and 11.46 mm (AITFL, IOM, PITFL, and deltoid, P < .0001, 95% CI 10.09-12.84). In group 2, the average baseline measurement for TFCS was 5.46 mm (P < .0001, 95% CI 4.95-5.97). With this sequence of transection, there was a less predictable increase in TFCS. With both deltoid transection alone and deltoid and PITFL transection, the TFCS actually decreased to an average of 5.38 mm (P < .0001, 95% CI 4.29-6.46) and 5.34 mm (P < .0001, 95% CI 4.25-6.43), respectively. With higher degrees of ligament involvement (i.e., deltoid, PITFL, and IOM, and all 4 ligaments transected), the TFCS increased to 6.08 mm (P < .0001, 95% CI 4.83-7.33) and 11.10 mm (P < .0001, 95% CI 9.2612.94), respectively. Although there was a statistically significant difference in TFCS between intact and single-ligament (AITFL) disruption specimens (P ¼ .0076, 95% CI 0.29-1.11), it approached but did not reach statistical significance comparing intact to double- or tripleligament disruption specimens (P ¼ .067, 95% CI 1.70 to 0.18, P ¼ .067, 95% CI 5.05 to 0.57). There was a statistically significant difference in TFCS when comparing intact to complete ligament transection models (P < .0001, 95% CI 4.66-8.82). Statistical significance was reached for 2-ligament versus complete transection specimens (P < .0001, 95% CI 4.467.34) but not for 2- versus 3-ligament disruption models (P ¼ .09, 95% CI 3.83 to 0.11). Medial Clear Space. The average MCS for groups 1 and 2 was 4.00 mm (P < .0001, 95% CI 3.13-4.87) and 4.78 mm (P < .0001, 95% CI 3.91-5.65), respectively. In group 1, progressive ligament transection beginning with the AITFL resulted in MCS measurements of 3.96 mm
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Fig 2. (A) Syndesmosis intact and 2-mm probe unable to fit in the anterior syndesmosis. (B) AITFL transected, 2.5-mm probe within the syndesmosis. (C) AITFL and IOM transected, 3-mm probe able to fit within the syndesmosis. (D) AITFL, IOM, and PITFL transected, 5-mm probe within syndesmosis. (E) AITFL, IOM, PITFL, and deltoid transected, with 5-mm probe in the syndesmosis. (AITFL, anteroinferior tibiofibular ligament; IOM, interosseous membrane; PITFL, posteroinferior tibiofibular ligament.)
(AITFL, P < .0001, 95% CI 3.28-4.64), 5.04 mm (AITFL and IOM, P < .0001, 95% CI 3.93-6.15), 5.73 mm (AITFL, IOM, and PITFL, P < .0001, 95% CI 4.49-6.98), and 9.82 mm (P < .0001, 95% CI 8.11-11.53) with all 4 syndesmotic ligaments disrupted. Group 2 corresponding values were the following: 4.92 mm (P < .0001, 95% CI 4.17-5.67), 5.64 mm (P < .0001, 95% CI 5.02-6.27), 5.76 mm (P < .0001, 95% CI 4.74-6.78), and 10.28 mm (P < .0001, 95% CI 7.34-13.20). MCS approached but was unable to detect statistically significant differences between intact and single/ double-ligament transection (P ¼ .82, 95% CI 0.32 to 0.40, and P ¼ .10, 95% CI 2.02 to 0.04, respectively). MCS was able to distinguish statistically significant differences between intact and 3- and 4-ligament transections (P ¼ .006, 95% CI 0.75-2.70, and P < .0001, 95% CI 4.12-7.52). The difference in MCS approached but did not reach significance with regards to single- (AITFL) and double-ligament (AITFL, IOM) disruption models (P ¼ .06, 95% CI 1.96 to 0.20). It did, however, reach significance with regard to distinguishing single- versus 3- and 4-ligament transection specimens (P ¼ .0009, 95% CI 0.93-2.62, and P < .0001, 95% CI 4.33-7.39, respectively). Similarly, MCS measurements approached but did not reach statistical significance in distinguishing 2versus 3-ligament transection (P ¼ .06, 95% CI 0.15
to 1.23); however, MCS reached significance in differentiating specimens with 2 versus 4 ligaments transected (P < .0001, 95% CI 3.70-5.86). Arthroscopic Measurements Although measurements were obtained in specimens with and without traction, the results obtained in these 2 samples were not significantly different. Therefore, only the data from the group without traction was used for final analysis. Anterior Probing In specimens with an intact syndesmosis, the average probe size able to be placed into the anterior syndesmosis was 0.90 mm (P ¼ .04, 95% CI 0.06-1.74) in group 1 and 0.80 mm (P ¼ .0001, 95% CI 0.44-1.17) in group 2. In group 1, this value increased with sequential ligament transection to 3.00 mm (AITFL, P < .0001, 95% CI 2.25-3.75), 3.80 mm (AITFL and IOM, P ¼ .05, 95% CI 3.06-4.54), 5.00 mm (AITFL, IOM, and PITFL, P < .0001), and 5.00 mm (AITFL, IOM, PITFL, and deltoid, P < .0001). In group 2, the corresponding values were 1.60 mm (deltoid, P ¼ .001, 95% CI 0.672.53), 2.00 mm (deltoid and PITFL, P ¼ .004, 95% CI 0.71-3.29), 2.30 mm (deltoid, PITFL, and IOM, P ¼ .002, 95% CI 0.89-3.70), and 4.90 mm with complete ligament transection (P ¼ .0004, 95% CI 4.71-5.08).
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Table 2. Parameter Measurements During Each Stage of Transection in Group 1 and Group 2 Group 1 Parameter TFO TFCS MCS AP PP
4.94 4.72 4.00 0.90 2.65
Intact (4.29-5.59) (3.52-5.91) (3.13-4.87) (0.06-1.74) (2.01-3.29)
þAITFL 4.40 (3.46-5.90) 5.42 (4.51-6.33) 3.96 (3.28-4.64) 3.00 (2.25-3.75) 3.60 (2.93-4.27)
2.80 5.56 5.04 3.80 4.40
þIOM (2.39-3.20) (4.77-6.35) (3.93-6.15) (3.06-4.54) (3.95-4.85)
1.47 7.53 5.73 5.00 5.00
þPITFL (0.07-2.86) (5.89-9.17) (4.49-6.98) (NA) (NA)
<0 11.46 9.82 5.00 5.00
þDeltoid (NA) (10.09-12.84) (8.11-11.53) (NA) (NA)
Group 2 Parameter TFO TFCS MCS AP PP
Intact 4.68 5.46 4.78 0.80 2.15
(3.46-5.90) (4.95-5.97) (3.91-5.65) (0.44-1.17) (1.78-2.52)
þDeltoid 3.76 5.38 4.92 1.60 3.40
(2.97-4.55) (4.29-6.46) (4.17-5.67) (0.67-2.53) (2.61-4.12)
þPITFL 3.02 5.34 5.64 2.00 3.90
(2.03-4.00) (4.25-6.43) (5.02-6.27) (0.71-3.29) (3.20-4.63)
þIOM 2.18 6.08 5.76 2.30 4.30
(1.63-2.73) (4.83-7.33) (4.74-6.78) (0.89-3.70) (3.83-4.77)
þAITFL <0 11.10 10.28 4.90 4.90
(NA) (9.26-12.94) (7.34-13.20) (4.71-5.08) (4.71-5.08)
NOTE. All values are in millimeters, with 95% confidence intervals included in parentheses. Group 1 transection sequence: AITFL, IOM, PITFL, deltoid. Group 2 transection sequence: deltoid, PITFL, IOM, AITFL. AITFL, anteroinferior tibiofibular ligament; AP, anterior probe size; IOM, interosseous membrane; MCS, medial clear space; NA, not applicable; PITFL, posteroinferior tibiofibular ligament; PP, posterior probe size; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.
Anterior probe size (AP) reached statistical significance with regards to distinguishing between intact and AITFL transected specimens (P < .0001, 95% CI 1.59-2.61). AP was able to detect statistically significant differences comparing single-ligament (AITFL) with 2- (AITFL and IOM), 3- (AITFL, IOM, and PITFL), and 4-ligament (AITFL, IOM, PITFL, and deltoid) disruptions (P ¼ .0072, <.0001, and <.0001, 95% CIs 0.23-1.37, 1.25-2.75, and 0.93-2.75, respectively). In addition, statistically significant differences were observed between 2- and 3-ligament (P ¼ .002, 95% CI 0.46-1.94), as well as 2- and 4-ligament (P ¼ .02, 95% CI 0.46-1.94) transections but not between 3- and 4-ligament disruption models (P > .99). Posterior Probing In specimens with an intact syndesmosis, the average probe size able to be placed into the posterior syndesmosis was 2.65 mm (P < .0001, 95% CI 2.01-3.29) in group 1 and 2.15 mm (P < .0001, 95% CI 1.78-2.52) in group 2. In group 1, this value increased with sequential ligament transection to 3.60 mm (AITFL) (P < .0001, 95% CI 2.934.27), 4.40 mm (AITFL, IOM) (P < .0001, 95% CI 3.954.85), 5.00 mm (AITFL, IOM, PITFL) (P < .0001) and 5.00 mm (AITFL, IOM, PITFL, deltoid) (P < .0001). In group 2, the corresponding values were 3.40 mm (deltoid) (P < .0001, 95% CI 2.61-4.12), 3.90 mm (deltoid, PITFL) (P < .0001, 95% CI 3.20-4.63), 4.30 mm (deltoid, PITFL, IOM) (P < .0001, 95% CI 3.83-4.77) and 4.90 mm (deltoid, PITFL, IOM, and AITFL) (P < .0001, 95% CI 4.71-5.08). Posterior probe size, much like anterior probe size, was effective at detecting statistically significant
differences between intact and single-, double-, triple-, and complete ligament transections (P values .0006, <.0001, <.0001, and <.001, 95% CIs 0.53-1.37, 1.292.20, 1.71-2.99, and 1.71-2.99, respectively). Posterior probing also found statistically significant differences in probe size between single- and double-, triple-, and complete ligament transection models (P values .0075, .0010, and .0010, 95% CIs 0.33-1.27, 0.73-2.07, and 0.73-2.07, respectively). In addition, posterior probing was able to distinguish between 2- and 3-ligament (P ¼ .03, 95% CI 0.15-1.05) and 2- and 4-ligament (P ¼ .03, 95% CI 0.15-1.05) transections. Posterior probe size did not find significant differences between 3- and 4-ligament disruption models (P > .99). A summary of the radiographic and arthroscopic testing is shown in Tables 2 and 3, respectively, as well as Figures 3 and 4.
Discussion This study reveals that arthroscopy is capable of detecting differences in syndesmotic diastasis resulting from sequential ligament disruption. Although stress fluoroscopy is the most commonly used dynamic diagnostic modality, including intraoperatively, it has been shown to be inferior and unreliable in comparison. For example, TFO and MCS were unable to detect significant differences between intact and AITFLtransected specimens. And although TFCS was shown to be able to identify significant differences between intact and AITFL disruption, it was unable to detect significant differences between intact and 2/3-ligament disruption models. Arthroscopy was universally more reliable, especially in detecting subtle injuries, with
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QUANTIFICATION OF SYNDESMOTIC INSTABILITY Table 3. Individual Parameter’s Ability to Distinguish Between Various Levels of Ligament Transection in Group 1 Intact A. TFO Intact Single Double Triple Complete B. TFCS Intact Single Double Triple Complete C. MCS Intact Single Double Triple Complete D. AP Intact Single Double Triple Complete E. PP Intact Single Double Triple Complete
e e e e e e e e e e e e e e e
Single P ¼ .29 (0.48 to 1.56) e e e e P ¼ .0076 (0.29-1.11) e e e e P ¼ .82 (0.32 to 0.40) e e e e
Double P < .0001 (1.47-2.81) P ¼ .024 (0.58-2.62) e e e
Triple
Complete
P ¼ .0004 (1.98-4.97) P ¼ .0008 (1.60-4.26) P ¼ .17 (0.23 to 2.90) e e
P < .0001 (4.29-5.59) P < .0001 (3.63-5.17) P < .0001 (2.39-3.20) P ¼ .13 (0.07 to 2.86) e
P ¼ .067 (0.18 to 1.70) P ¼ .56 (0.63 to 0.36) e e e
P ¼ .067 (0.57 to 5.05) P ¼ .058 (0.07 to 4.31) P ¼ .09 (0.11 to 3.83) e e
P P P P
< < < <
.0001 .0001 .0001 .0001
(4.66-8.82) (4.15-7.93) (4.46-7.34) (2.59-5.27) e
P ¼ .10 (2.02 to 0.04) P ¼ .06 (1.96 to 0.20) e e e
P ¼ .006 (0.75-2.70) P ¼ .0009 (0.93 to 2.62) P ¼ .06 (0.15 to 1.23) e e
P P P P
< < < <
.0001 .0001 .0001 .0001
(4.12-7.52) (4.33-7.39) (3.70-5.86) (3.30-4.87) e
e e e e e
P < .0001 (1.59-2.61) e e e e
P < .0001 (2.37-3.43) P ¼ .0072 (0.23-1.37) e e e
P < .0001 (3.26-4.94) P < .0001 (1.25-2.75) P ¼ .002 (0.46-1.94) e e
P < .0001 (3.26-4.93) P < .0001 (0.93-2.75) P ¼ .02 (0.46-1.94) P > .99 e
e e e e e
P ¼ .0006 (0.53-1.37) e e e e
P < .0001 (1.29-2.20) P ¼ .0075 (0.33-1.27) e e e
P < .0001 (1.71-2.99) P ¼ .001 (0.73-2.07) P ¼ .03 (0.15-1.05) e e
P < .0001 (1.71-2.99) P ¼ .001 (0.73-2.07) P ¼ .03 (0.15-1.05) P > .99 e
NOTE. Single ¼ AITFL; Double ¼ AITFL/IOM; Triple ¼ AITFL/IOM/PITFL; Complete ¼ AITFL/IOM/PITFL/deltoid. Values within parentheses are 95% confidence intervals. Group 1 was chosen for presentation as this sequence represents a clinical mechanism of injury (supinationexternal rotation). Of the radiographic parameters, only TFCS was able to distinguish between intact and AITFL-transected specimens; however, TFCS did not reveal significance between intact and double- or triple-ligament transection. Arthroscopic probing was universally better at distinguishing between sequential levels of ligament injury and was only unable to distinguish between 3- and complete ligament transection models. AITFL, anteroinferior tibiofibular ligament; AP, anterior probe size; IOM, interosseous membrane; MCS, medial clear space; PITFL, posteroinferior tibiofibular ligament; PP, posterior probe size; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.
Fig 3. Group 1. There was minimal difference in radiographic measurements obtained after 1 ligament was transected whereas the difference was significant between intact and AITFL sectioned specimens using arthroscopy. Radiographs were clearly influenced by successive syndesmotic disruption but stress views were not able to distinguish between intact and single-ligament disruption. Asterisks represent statistically significant measurements (P < .05). (AITFL, anteroinferior tibiofibular ligament; IOM, interosseous membrane; MCS, medial clear space; PITFL, posteroinferior tibiofibular ligament; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.)
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Fig 4. Group 2. Similarly, in group 2, arthroscopy could identify statistically significant differences between intact and deltoidtransected specimens, and between sequential ligamentous transection. Radiographs could not identify a significant difference until at least 3 ligaments had been transected. Asterisks indicate statistically significant measurements (P < .05). (IOM, interosseous membrane; MCS, medial clear space; PITFL, posteroinferior tibiofibular ligament; TFCS, tibiofibular clear space; TFO, tibiofibular overlap.)
both anterior and posterior probing being able to distinguish between intact and AITFL-transected specimens. In addition, arthroscopy is able to distinguish between most sequential injury patterns, that is, intact versus single-ligament, single- versus double-ligament, and double- versus triple-ligament transections. Only 3- and 4-ligament disruption models were unable to be distinguished with arthroscopic probing. Syndesmotic injury is a broad term with significant variability in the extent of soft tissue and ligamentous involvement, associated fracture and resulting ankle instability. Historically, optimal indications for treatment of these injuries has been difficult to determine because of an incomplete understanding of the clinical implications associated with varying degrees of ligamentous damage. The authors found no study that has used arthroscopy to quantify the amount of instability resulting from injury to single ligaments such as the AITFL or deltoid, or whether arthroscopy is capable of detecting differences in syndesmotic widening between different injury patterns. This information is important from both a research and clinical perspective, as each individual ligament does not contribute equally to the stability of the ankle mortise. Thus, “syndesmotic injury” as a broad term should be thought of according to changes in stability resulting from various combinations of ligament involvement. One must also make the distinction between ligament injury and syndesmotic instability. In a cadaveric study by Ogilvie-Harris et al., the contribution of each syndesmotic ligament to ankle stability was calculated. The authors found that the AITFL, IOM, and PITFL provided 35%, 22%, and 42% of total ankle stability, respectively.10 Although the PITFL contributes
nearly half of the resistance to syndesmotic diastasis, isolated injuries to the PITFL are rare. A study by Oae et al. evaluated magnetic resonance imaging (MRI) for diagnosis of syndesmotic injuries and found that only 5 of 28 patients with a syndesmotic injury had a PITFL injury, and no patient had an isolated PITFL injury. On the other hand, all patients with a syndesmotic injury had an AITFL injury.11 Similarly, a study by Takao et al.7 revealed that all patients diagnosed with syndesmotic injury by arthroscopic means had injury to the AITFL, whereas less than 50% had PITFL injury and no patients were found to have an isolated PITFL injury. Thus, it is possible that injury to the AITFL in isolation or in combination with IOM injury may produce subtle yet clinically relevant instability previously missed by clinical exam and stress radiography. Making the diagnosis of syndesmotic instability can be challenging and yet is critically important for providing adequate treatment for patients. It has been shown that clinical examination findings, preoperative stress radiographs, and intraoperative fluoroscopy are insufficient in identifying all syndesmotic injuries.3,6,12-16 The literature regarding the utility of MRI in the diagnosis of syndesmotic injury is promising, with nearly 100% sensitivity across all studies.17,18 However, there is potential for false positive results, and MRI provides a static image of instability, a process that is dynamic in nature.19 Therefore, arthroscopy has been introduced as both a possible diagnostic and therapeutic tool when dealing with these injuries. In this study, stress fluoroscopy was generally worse than arthroscopy at identifying changes in syndesmotic diastasis between various levels of ligamentous involvement, particularly when only 1 or 2 ligaments were transected. Use of
QUANTIFICATION OF SYNDESMOTIC INSTABILITY
stress radiography/fluoroscopy as the sole means of determining syndesmotic stability may lead to missing a significant number of lower-grade injuries involving, for example, only the AITFL or AITFL/IOM. The clinical and prognostic implications of varying degrees of syndesmotic ligament involvement are also poorly understood, although with the increasing use of arthroscopy and MRI it is now possible to evaluate subtle syndesmotic injuries that may have previously been overlooked in the setting of acute and chronic injury.20 Beginning to study these modalities to quantify the extent of damage and resulting instability is paramount in the process of developing objective methods for arthroscopic evaluation of the syndesmosis. In 2001, Takao et al. presented data on the ability of radiography (AP and mortise) and arthroscopy to detect syndesmotic diastasis in 38 Weber B ankle fractures. Although arthroscopy was able to detect injury in 87% of patients, AP and mortise radiographs identified syndesmotic injury in only 42% and 55%, respectively.16 In 2003, the same group was able to report on the improved diagnostic accuracy of arthroscopy, with 100% of syndesmotic injuries detected versus 63% with standard radiography.7 Liu and colleagues further explored the capability of arthroscopic evaluation of the syndesmosis in 2005 by comparing intraoperative stress radiography and arthroscopy in 53 Weber B and C ankle fractures. This was the first study to report instability in multiple planes (coronal, sagittal, and rotational). Stress views identified 16 cases of diastasis, whereas arthroscopy was able to identify an additional 19 cases using 2 mm of translation in any plane as a threshold for instability. All syndesmotic injuries were treated with screw fixation and subsequent removal at 12 weeks. Arthroscopy was repeated at the time of screw removal, and syndesmotic ligament healing was observed in all cases and no further evidence of instability was noted. However, the authors comment that there is a continued role for intraoperative stress radiography, as arthroscopy is incapable of assessing complex fibular “fracture reduction and proper restoration of fibular length and longitudinal orientation of the syndesmosis.”6 In a recent study by Watson and colleagues, arthroscopic evaluation of cadaveric below-knee specimens was able to detect multiplanar syndesmotic instability in the transverse, sagittal, and coronal planes by applying increasing forces and measuring the amount of fibular displacement that resulted. Four ligament disruption models were chosen for analysis: intact, AITFL/IOM, AITFL/IOM/ATFL/CFL, and AITFL/IOM/ATFL/CFL/ PITFL/TL disruption.21 The ligament transection model used for the current study differs from the aforementioned analysis in several regards. The basis for this model is predicated by the work of Stoffel and
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colleagues,15 with 2 groups representing transection in reverse directions beginning with either the AITFL (group 1) or deltoid ligament (group 2). We did not perform ATFL/CFL transection, as these lateral ligaments are not considered primary restraints to syndesmotic diastasis and typically are not involved when injury to the syndesmotic ligamentous complex is present.22 In addition, solitary AITFL transection was performed to evaluate whether injury to this ligament results in instability, and to determine if this can be appreciated arthroscopically. Deltoid ligament disruption was included for 2 reasons. This ligament is often injured in conjunction with mechanisms leading to syndesmosis injury (e.g., SER4 deltoid). Furthermore, repair in the setting of bimalleolar equivalent ankle fracture has been shown to confer stability comparable to syndesmotic screw fixation, indicating that the deltoid may have a role in providing restraint to syndesmotic diastasis.1 Finally, cadaveric above-knee amputation specimens were used, as this maintained the integrity of the IOM and the gastrocsoleus complex. We also chose to transect the ligaments in 2 groups in different order to decrease the possibility that repetitive measurements could increase the syndesmotic diastasis inadvertently. The current study performed arthroscopic examinations both with and without traction, and found no significant differences in final measurements between the 2 groups. Therefore, only the data regarding arthroscopic probe examination without traction was used for final analysis. However, it is important to note that consistency in the use or avoidance traction during syndesmotic probing should be maintained so the examiner has a reproducible baseline for the syndesmotic appearance. Limitations There are several limitations to the current study. Cadaver specimens and a small sample size were used for the study. No power analysis was performed prior to beginning the study, thus making the potential for insufficient power a possibility. Only the major ligamentous contributors to the syndesmosis were studied; it is possible that there are additional minor soft tissue restraints such as the ATFL and CFL that may contribute to overall stability. Investigators were not blinded to the level of ligament injury, adding a potential for observation bias. Finally, although each ankle was examined for evidence of chronic injury and arthritic changes, there were no available data regarding prior ankle injury and subsequent treatment.
Conclusions Stress radiography did not distinguish between intact and single-ligament disruption and were unreliable in distinguishing between sequential transection models.
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Arthroscopy significantly predicted isolated disruption of the AITFL or deltoid ligaments. Also, probing was able to differentiate between most patterns of ligament injury, including sequential transections.
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