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Kinematic TKA using navigation: Surgical technique and initial results
Orthopaedics & Traumatology: Surgery & Research 102 (2016) 99–104
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Original article
Kinematic TKA using navigation: Surgical technique and initial results J.R.B. Hutt , M.-A. LeBlanc , V. Massé , M. Lavigne , P.-A. Vendittoli ∗ Université de Montréal, Hôpital Maisonneuve-Rosemont, Department of Surgery, 5415 boulevard de l’Assomption, Montréal, QC H1T 2M4, Canada
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Article history: Received 20 February 2015 Accepted 5 November 2015 Keywords: Knee Arthroplasty Navigation TKA Technique Outcomes Kinematic
a b s t r a c t Background: Kinematic alignment for total knee arthroplasty (TKA) may be one way of improving outcomes. Previous studies have either used patient-specific instrumentation, which adds cost, or standard instrumentation, which provides no intraoperative feedback on resection alignment. Hypothesis: To determine if computer navigation could reproduce native patient anatomy and simplify ligament balance during TKA whilst giving satisfactory improvements in functional scores at early followup. Materials and methods: Computer navigation was used for kinematic distal femoral and proximal tibial cuts in 100 consecutive and unselected TKAs. Resections were modified only if measured angles fell outside a pre-defined safe range of combined coronal orientation within ± 3 degrees of neutral and/or independent femoral or tibial cuts within ± 5 degrees. Pre- and postoperative measurements of the hipknee-ankle (HKA) angle, the lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA) were taken using long-leg standing radiographs. Clinical evaluation was with the WOMAC and KOOS scales. Results: Mean follow-up was 2.4 years (range 1.0–3.7, SD 0.8). The mean pre-op LDFA was 2.1 degrees valgus (9.2 valgus to 3.7 varus, SD 2.5) and 1.8 degrees valgus post-op (5.7 valgus to 4.2 varus, SD 2.0) (P = 0.41). The mean pre-op MPTA was 3.0 degrees varus (10.6 valgus to 10.2 varus, SD 3.2) and 2.4 degrees varus post-op (4.0 valgus to 6.8 varus, SD 2.2) (P = 0.03). The mean WOMAC score improved from 49.4 (29–85, SD 12.8) to 24.7 (0–73, SD 16.5) (P < 0.001) and the mean KOOS score from 37.1 (7.2–77.2, SD 13.0) to 65.1 (26.8–100, SD 16) (P < 0.001). Five knees (5%) required additional ligament release, four with valgus OA and one with varus OA. Two knees (2%) required lateral retinacular release for patellar tracking. Discussion: Computer navigation for kinematic TKA provides the operating surgeon with full control and feedback at each step, whilst also allowing partial correction of more extreme anatomy that might be unsuitable for recreation during TKA. This technique helps to preserve ligament isometry and produces satisfactory improvements in functional scores. Level of evidence: IV (retrospective case series review). © 2015 Elsevier Masson SAS. All rights reserved.
1. Introduction The most common practice for alignment in total knee arthroplasty (TKA) creates a neutral lower limb axis by cutting distal femoral and proximal tibial bone perpendicular to the mechanical axes, with the femoral component placed in external rotation to achieve ligament balance in flexion (mechanical alignment technique) [1]. TKAs implanted in this manner have established long term survivorship [2–4]. On the other hand, this method alters joint line orientation when compared with many patients’ native anatomy [5–8]: Furthermore, not all patients will recover normal knee function and limitations persist; dissatisfaction is reported ∗ Corresponding author. Tel.: +1 514 246 0068; fax: +1 514 252 0115. E-mail address: [email protected] (P.-A. Vendittoli). http://dx.doi.org/10.1016/j.otsr.2015.11.010 1877-0568/© 2015 Elsevier Masson SAS. All rights reserved.
in up to 20% of patients [9,10]. Kinematic alignment is an alternative option; bone cuts are made to replace and resurface the native joint, preserving the natural knee anatomy. This aligns the components with the three kinematic axes [11], maintaining the soft tissue envelope and minimising the need for ligament release [8,11,12]. However, there remains a question of whether all native patient anatomy is suitable for current TKA biomechanics and fixation in the long term. Other short-term studies have demonstrated that variations in alignment with kinematic TKA do not lead to early failure, or impact proxies of long-term outcome issues such as unfavourable contact kinematics [13,14]. That said, there remains a question of whether all patients are suitable for kinematic alignment; some native anatomy may be inherently biomechanically inferior, predisposing both to initial disease and then potentially to prosthetic complications if recreated during TKA. In fact, the
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effect of TKA alignment on eventual outcomes is still not completely understood. Some studies on mechanically aligned TKA have noted significant load variations [15] and higher failure rates with excessive outliers of joint line orientation [16–20]. Others have disputed the impact of coronal alignment of the limb on outcomes [21,22]. It is probable that improvements in design, fixation and biomaterial durability are also contributing, rendering modern TKA more forgiving of inaccuracy. Additionally, comparisons across series that do not give the ranges for both pre- and postoperative measurements should be made cautiously; accurate kinematic alignment in varus is very different to unplanned varus from surgical error when performing mechanical alignment. Additionally, a well-performed mechanically aligned TKA showing adequate coronal alignment can be the result of significant alteration of the orientation of the anatomical joint line and overall knee alignment from their preoperative state, requiring significant soft-tissue release to achieve a balanced implantation [12,23]. Such ligament releases lack accuracy and subtle instability will often remain [8]. All of these factors may impact the eventual mechanics and survivorship of the TKA. Most kinematic alignment reports use patient-specific instrumentation (PSI) to guide resection [12,13,24]. This requires additional preoperative imaging with CT or MRI and associated planning time from the surgeon. Evidence suggests that although operating room efficiency can benefit, the overall effect is cost increases [25–27]. Howell et al. describe a kinematic technique using generic TKA instrumentation with measured resections [28]. The disadvantage here is that the surgeon cannot accurately judge intraoperatively the implantation angles that result. Until we know more about the effect of various alignments on long-term outcomes, especially at the extremes, this could be seen as a potential risk. One unexplored avenue to achieving kinematic alignment is navigation. This technique has the potential benefit of giving the surgeon the ability to accurately define both patient anatomy and the position of the implants intraoperatively. This study describes a novel technique for performing kinematic TKA within certain limits using computer navigation. Our hypotheses for the study were that kinematic alignment using navigation would: • reproduce patients’ pre-arthritic anatomy as measured on comparative pre- and postoperative radiographs, and require minimal intraoperative ligament releases to balance the TKA and; • produce satisfactory improvements in functional scores at early follow-up.
curve of this technique. All patients received a cruciate-retaining, fixed bearing implant (Triathlon, Stryker, MI, US). The approach was an anterolateral skin incision [29] and medial parapatellar arthrotomy in all cases, without tourniquet. Regardless of preoperative deformity, only the deep MCL was released routinely. The patella was subluxed laterally. Kinematic alignment in the coronal plane was achieved using optical computer navigation (Orthomap ASM, Stryker, Michigan). The goal of the procedure was to resurface the knee according to each patient’s normal anatomy and therefore maintain the femoral flexion axis. Distal femoral and proximal tibial cuts were adjusted to ensure a 9 mm resection on the intact femoral condyle and tibial plateau, representing the TKA implant thickness. Cartilage and bone loss on the distal femoral condyle and tibial plateau was assessed by comparison with intact areas. On the worn side, fully exposed subchondral bone was considered to represent 3 mm of cartilage loss [30]. The coronal resection angles were then adjusted to compensate for the loss. For example, in a varus knee with full cartilage loss on the medial condyle and intact lateral side, medial resection would have been 6 mm and 9 mm laterally thus recreating the patient’s native joint orientation. When partial thickness wear was present, we had to estimate the thickness loss at 1 or 2 mm and adjust the resection accordingly. In all cases, preoperative planning was performed on long films and angles were compared with intraoperative measurements to rule out gross miscalibration of the navigation equipment, (which did not occur) and the final decisions were made on the intraoperative findings alone. Resections were modified from patient anatomy only if the measured angles fell outside a pre-defined “safe range” of either a combined coronal orientation within ± 3 degrees of neutral and/or independent femoral or tibial cuts within ± 5 degrees. An example tibial resection is shown in Figs. 1 and 2. Resection accuracy was confirmed by caliper measurements (Fig. 3). A similar procedure was followed for distal femoral resection. The remainder of the procedure was completed using standard TKA instrumentation. To resurface the posterior condyles, a posterior referencing guide was set to neutral rotation, thus resecting only the implant thickness of the posterior condyles and matching each patient’s native femoral rotation. Tibial component rotation was set relative to the trial femoral component with the knee in extension. Pre- and postoperative measurements of coronal orientation were taken using long-leg standing radiographs using the hipknee-ankle (HKA) angle, the lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA). The LDFA is the angle formed by the distal extent of the femur or femoral TKA component and the mechanical axis of the femur. The MPTA is the angle formed
2. Methods Our scientific and ethical committees approved the study and patient consent was obtained. One surgeon (PAV) performed all the operations. All patients presenting with degenerative arthritis of the knee and considered suitable for primary TKA were considered for inclusion. During this period, no other technique for TKA was used regardless of preoperative alignment, range of motion or the presence of fixed deformity. The only exclusion criteria was preoperative deformity or ligamentous incompetence that necessitated a higher level of constraint. The first 100 consecutive kinematic TKAs (95 patients, 5 bilateral procedures) with this technique were identified from our database. Patient demographics are shown in Table 1. This included all patients in the learning Table 1 Cohort demographics. M:F (%) BMI (Mean, Range, SD) Age (Mean, Range, SD)
32:63 (34%) 31 (19–47) 6 68 (38–89) 11
Fig. 1. Intraoperative photograph of the proximal tibia. The forceps tip is on the medial side, where there is full-thickness wear of the cartilage. Human knee cartilage thickness is between 2–3 mm [30]. To recreate the anatomical joint line, the resection therefore needs to be 2–3 mm less medially.
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Fig. 2. Comparative resections for the proximal tibia for mechanical and kinematic cuts.
3. Results
Fig. 3. Caliper measurement of proximal tibial resection after kinematic cuts. The calipers are on the lateral plateau.
by the mechanical axis of the tibia and the joint line or tibial base plate. Two evaluators (JH and MB) performed the measurements as described by previous authors [1,7,23]. Operative records were reviewed to establish the need for ligament release. Clinical scoring using WOMAC and KOOS scales was performed in the outpatient clinic. 2.1. Statistical analysis All calculations were performed using Prism V6.0 (Graphpad Software, US). Pre- and postoperative paired categorical data was compared using McNemar’s test (M:F ratio, number of outliers). Continuous data was tested for normality using the D’AgostinoPearson omnibus test and paired comparisons were performed using Student’s T-test (pre- and post-op LDFA, WOMAC and KOOS scores) or the Wilcoxon signed rank test (Age, BMI, pre- and post-op MPTA, pre- and post-op HKA).
The mean follow up was 2.4 years (range 1.0–3.7, SD 0.8). The pre- and postoperative measurements are shown in Table 2; valgus measurements are positive, varus measurements are negative. Fig. 4 shows the distribution of measurements for the LDFA and the MPTA. The paired comparison of these two angles are surrogates for recreation of native anatomy, unlike the HKA which preoperatively will reflect deformity due to cartilage loss. Pre-op, 15 knees had a LDFA of > 5◦ varus or valgus versus 4 post-op (P = 0.01). All these 4 post-op LDFAs outliers were in valgus at a mean of 5.3◦ (range 5.1–5.7). For the MPTA, 20 knees were in > 5◦ varus or valgus pre-op versus 12 post-op (P = 0.14). All these 12 post-op MPTAs outliers were in varus at a mean of 5.8◦ (range 5.2–6.8). The mean overall combined coronal orientation (HKA) was 0.5◦ varus (range −7.4 to 6.3, SD 2.3). Twelve knees were outliers regarding HKA, three in valgus (mean 3.5◦ , 3.2–3.9) and nine in varus (mean 3.8◦ , 3.2–4.8). We should know if these outliers correspond to pre-op marked deformity. The preoperative deformity as measured by the HKA was not significantly different between the outliers (mean 5.1◦ varus) and the non-outlier cases (mean 4.5◦ varus, P = 0.30). The differences for each individual knee from pre- to post-op are shown in Fig. 5. Only five knees (5%) required additional ligament release, four with valgus OA and one with varus OA. In these 5 knees, the patient’s anatomy felt outside our “safe range” of either a combined coronal orientation within ± 3 degrees of neutral and/or independent femoral or tibial cuts within ± 5 degrees. This may explain the need for additional ligament release. Two valgus knees (2%) required lateral retinacular release to allow satisfactory patellar tracking. The mean WOMAC score improved from 49.4 (29.0–85.0, SD 12.8) to 24.7 (0.0–73.0, SD 16.5) (P < 0.001). All KOOS scores were significantly improved (P < 0.001); pain from 38.5 (11.1–72.2, SD
Table 2 Pre- and postoperative measures of coronal alignment. Preoperative
HKA LDFA MPTA
Postoperative
P-value
Mean
Range
SD
Mean
Range
SD
−4.6 2.1 −3.0
−15.5–11.6 −3.7–9.2 −10.2–10.6
5.9 2.5 3.2
−0.5 1.8 −2.4
−7.4–6.3 −4.2–5.7 −6.8–4.0
2.3 2.0 2.2
HKA: hip-knee-ankle; LDFA: lateral distal femoral angle; MPTA: medial proximal tibial angle.
< 0.001 0.41 0.03
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Fig. 4. Histogram distribution of pre and postoperative LDFA and MPTA. The shaded area indicates the safe zone.
17.0) to 74.6 (22.0–100, SD 18.8), symptom from 39.4 (10.7–67.9, SD 12.6) to 54.8 (18.0–100, SD 26.7), ADL from 41.2 (0–86.8, SD 18.7) to 76 (25.0–100, SD 19.3), sport from 14.2 (0–100, SD 22.7) to 46.4 (0–100, SD 30.6) and quality of life from 24.1 (0–62.5, SD 18.2) to 71.9 (19–100, SD 23.1). 4. Discussion TKA outcomes have not yet reached the consistent high levels seen with total hip arthroplasty [10]. Kinematic alignment may be one solution improving patient satisfaction and function. This study evaluates a novel method using computer navigation to perform kinematic TKA and preserving patient knee anatomy within a defined threshold. Our hypotheses for the study were that kinematic alignment using navigation would: • reproduce patient anatomy as measured on comparative pre- and postoperative radiographs, and require minimal intraoperative ligament releases to balance the TKA and; • produce satisfactory improvements in functional scores at early follow-up. The results demonstrate that the technique is reproducible; it permits recreation of native anatomy within a certain range, whilst allowing for corrections when desired. The technique also has the advantage of allowing the surgeon to know the exact orientation of bony resection without the need for the additional imaging, planning and cost associated with PSI. The use of navigation has the potential for increasing operative time and costs, the latter mainly from additional training and equipment expenditure [31]. However, as this technique navigates only the coronal cuts, in a hospital setting where surgeons and
staff have considerable experience with navigation equipment, we believe this effect is minimised. Although clinical benefit remains unproven in mechanical TKA, navigation has been shown to be an accurate technique for prosthesis alignment, reducing outliers for the targeted orientation [32,33]. In terms of the alignment, there was a significant difference between pre and postoperative HKA limb alignment (4.6 to 0.5 varus, P < 0.001, Fig. 5), which is to be expected due to the effect of restoring cartilage and bone loss. Postoperatively, only 12 knees had a combined coronal orientation outside the safe range of ± 3 degrees, three in valgus (mean 3.5◦ , 3.2–3.9) and nine in varus (mean 3.8◦ , 3.2–4.8). Outliers from our safe range probably occurred as a result of slight imprecision in the navigation system, or small variations during bone cuts or implant cementation. On the femoral side, the comparative data suggests we were able to recreate the distal femoral anatomy, an important step in kinematic alignment to maintain the anatomic femoral flexion axis. Maintaining this axis is a key feature of kinematic TKR; this is why ideally no additional rotation is given to the femoral implant. However, a number of femora required a small correction to bring the measurements into our safe range; 15 knees had a pre-op LDFA of > 5 deg, reduced to only 4 knees post-op (P = 0.01). A total of 2/4 (50%) in this latter category were under corrected from pre-op. Most of the significant corrections were performed on the tibial side. The preoperative MPTA range was from 10.6 valgus to 10.2 varus, reduced to 4.0 valgus to 6.8 varus postop. Although not statistically significant, fewer cases were outside of safe range postoperatively, with 12 cases at greater than ± 5◦ post-op versus 20 cases pre-op (P = 0.14). A total of 6/12 (50%) of the cases with post-op values outside the safe range were under corrected from pre-op. Overall, individual changes in alignment angles, represented in Fig. 5, demonstrate that the described technique reliably brought these measurements to within the desired
Fig. 5. Individual corrections for HKA, LDFA and MPTA. The shaded area indicates the safe zone.
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limits. With corrections, the post-op measured angles and overall alignment in this study showed ranges and standard deviations similar to both normal anatomy in asymptomatic volunteers as well as to other reports of component orientation after kinematic TKA [13,23,24]. This probably results from the fact that the majority of patients’ normal anatomy, certainly in this cohort, falls within the self-imposed limits of this technique. Only 5% of our cohort required ligament release for a balanced implantation. Other series of kinematic TKA have recorded the need for ligament release [24,28], the valgus knee remains problematic; the need for further balancing is not completely eliminated in these patients with kinematic alignment. In another similar size series, Howell et al. report a need for release of lateral structures in 17% of their patients [28]. This factor is affected by nuances in technique; the study by Howell et al. also incorporates modified tibial resection for coronal balance, and this study has self-imposed alignment boundaries. Both of these will have subtle effects on the need for ligament balancing. Our study has limitations. Despite its frequent use in published literature, a single coronal measurement is not a completely adequate way of assessing alignment even with standardised radiography. The numbers are relatively small, and therefore cannot be completely representative of anatomical variation in TKA patients. Although there were no early failures in this cohort, we cannot make inferences about the effect of this technique on long-term function or survivorship. At the time of writing, published comparisons between the two techniques are few, with only one randomised study in the literature. Dossett et al. found that despite the expected variations in femoral and tibial component obliquity, both kinematic and mechanically aligned TKAs showed similar results in overall alignment at the earlier follow-up point [24], although better outcome scores were seen in the kinematic group at two years [34]. Other case series have shown good functional outcomes for kinematic TKA [13,28], but there is limited long-term data; the question of whether it can provide better clinical function and satisfaction while maintaining the long term survivorship offered by classical mechanically aligned TKA is currently unanswered. Long term cohort studies, radio steriometric analysis studies, and further randomised trials are warranted. In conclusion, this study demonstrates that using computer navigation allows the operating surgeon to perform kinematic TKA by restoring knee anatomy in most cases and partially correcting some extreme anatomy that might be unsuitable for recreation with TKA. Further studies should be undertaken to determine the safe orientation and alignment boundaries associated with TKAs implanted with differing alignment philosophies. Funding No funding was received for this study. Disclosure of interest The authors declare that they have no competing interest. References [1] Cherian JJ, Kapadia BH, Banerjee S, Jauregui JJ, Issa K, Mont MA. Mechanical, anatomical, and kinematic axis in TKA: concepts and practical applications. Curr Rev Musculoskelet Med 2014;7:89–95, http://dx.doi.org/10.1007/ s12178-014-9218-y. [2] Rodricks DJ, Patil S, Pulido P, Colwell CW. Press-fit condylar design total knee arthroplasty. Fourteen to seventeen-year follow-up. J Bone Joint Surg Am 2007;89:89–95, http://dx.doi.org/10.2106/JBJS.E.00492.
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Original article
Kinematic TKA using navigation: Surgical technique and initial results J.R.B. Hutt , M.-A. LeBlanc , V. Massé , M. Lavigne , P.-A. Vendittoli ∗ Université de Montréal, Hôpital Maisonneuve-Rosemont, Department of Surgery, 5415 boulevard de l’Assomption, Montréal, QC H1T 2M4, Canada
a r t i c l e
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Article history: Received 20 February 2015 Accepted 5 November 2015 Keywords: Knee Arthroplasty Navigation TKA Technique Outcomes Kinematic
a b s t r a c t Background: Kinematic alignment for total knee arthroplasty (TKA) may be one way of improving outcomes. Previous studies have either used patient-specific instrumentation, which adds cost, or standard instrumentation, which provides no intraoperative feedback on resection alignment. Hypothesis: To determine if computer navigation could reproduce native patient anatomy and simplify ligament balance during TKA whilst giving satisfactory improvements in functional scores at early followup. Materials and methods: Computer navigation was used for kinematic distal femoral and proximal tibial cuts in 100 consecutive and unselected TKAs. Resections were modified only if measured angles fell outside a pre-defined safe range of combined coronal orientation within ± 3 degrees of neutral and/or independent femoral or tibial cuts within ± 5 degrees. Pre- and postoperative measurements of the hipknee-ankle (HKA) angle, the lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA) were taken using long-leg standing radiographs. Clinical evaluation was with the WOMAC and KOOS scales. Results: Mean follow-up was 2.4 years (range 1.0–3.7, SD 0.8). The mean pre-op LDFA was 2.1 degrees valgus (9.2 valgus to 3.7 varus, SD 2.5) and 1.8 degrees valgus post-op (5.7 valgus to 4.2 varus, SD 2.0) (P = 0.41). The mean pre-op MPTA was 3.0 degrees varus (10.6 valgus to 10.2 varus, SD 3.2) and 2.4 degrees varus post-op (4.0 valgus to 6.8 varus, SD 2.2) (P = 0.03). The mean WOMAC score improved from 49.4 (29–85, SD 12.8) to 24.7 (0–73, SD 16.5) (P < 0.001) and the mean KOOS score from 37.1 (7.2–77.2, SD 13.0) to 65.1 (26.8–100, SD 16) (P < 0.001). Five knees (5%) required additional ligament release, four with valgus OA and one with varus OA. Two knees (2%) required lateral retinacular release for patellar tracking. Discussion: Computer navigation for kinematic TKA provides the operating surgeon with full control and feedback at each step, whilst also allowing partial correction of more extreme anatomy that might be unsuitable for recreation during TKA. This technique helps to preserve ligament isometry and produces satisfactory improvements in functional scores. Level of evidence: IV (retrospective case series review). © 2015 Elsevier Masson SAS. All rights reserved.
1. Introduction The most common practice for alignment in total knee arthroplasty (TKA) creates a neutral lower limb axis by cutting distal femoral and proximal tibial bone perpendicular to the mechanical axes, with the femoral component placed in external rotation to achieve ligament balance in flexion (mechanical alignment technique) [1]. TKAs implanted in this manner have established long term survivorship [2–4]. On the other hand, this method alters joint line orientation when compared with many patients’ native anatomy [5–8]: Furthermore, not all patients will recover normal knee function and limitations persist; dissatisfaction is reported ∗ Corresponding author. Tel.: +1 514 246 0068; fax: +1 514 252 0115. E-mail address: [email protected] (P.-A. Vendittoli). http://dx.doi.org/10.1016/j.otsr.2015.11.010 1877-0568/© 2015 Elsevier Masson SAS. All rights reserved.
in up to 20% of patients [9,10]. Kinematic alignment is an alternative option; bone cuts are made to replace and resurface the native joint, preserving the natural knee anatomy. This aligns the components with the three kinematic axes [11], maintaining the soft tissue envelope and minimising the need for ligament release [8,11,12]. However, there remains a question of whether all native patient anatomy is suitable for current TKA biomechanics and fixation in the long term. Other short-term studies have demonstrated that variations in alignment with kinematic TKA do not lead to early failure, or impact proxies of long-term outcome issues such as unfavourable contact kinematics [13,14]. That said, there remains a question of whether all patients are suitable for kinematic alignment; some native anatomy may be inherently biomechanically inferior, predisposing both to initial disease and then potentially to prosthetic complications if recreated during TKA. In fact, the
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effect of TKA alignment on eventual outcomes is still not completely understood. Some studies on mechanically aligned TKA have noted significant load variations [15] and higher failure rates with excessive outliers of joint line orientation [16–20]. Others have disputed the impact of coronal alignment of the limb on outcomes [21,22]. It is probable that improvements in design, fixation and biomaterial durability are also contributing, rendering modern TKA more forgiving of inaccuracy. Additionally, comparisons across series that do not give the ranges for both pre- and postoperative measurements should be made cautiously; accurate kinematic alignment in varus is very different to unplanned varus from surgical error when performing mechanical alignment. Additionally, a well-performed mechanically aligned TKA showing adequate coronal alignment can be the result of significant alteration of the orientation of the anatomical joint line and overall knee alignment from their preoperative state, requiring significant soft-tissue release to achieve a balanced implantation [12,23]. Such ligament releases lack accuracy and subtle instability will often remain [8]. All of these factors may impact the eventual mechanics and survivorship of the TKA. Most kinematic alignment reports use patient-specific instrumentation (PSI) to guide resection [12,13,24]. This requires additional preoperative imaging with CT or MRI and associated planning time from the surgeon. Evidence suggests that although operating room efficiency can benefit, the overall effect is cost increases [25–27]. Howell et al. describe a kinematic technique using generic TKA instrumentation with measured resections [28]. The disadvantage here is that the surgeon cannot accurately judge intraoperatively the implantation angles that result. Until we know more about the effect of various alignments on long-term outcomes, especially at the extremes, this could be seen as a potential risk. One unexplored avenue to achieving kinematic alignment is navigation. This technique has the potential benefit of giving the surgeon the ability to accurately define both patient anatomy and the position of the implants intraoperatively. This study describes a novel technique for performing kinematic TKA within certain limits using computer navigation. Our hypotheses for the study were that kinematic alignment using navigation would: • reproduce patients’ pre-arthritic anatomy as measured on comparative pre- and postoperative radiographs, and require minimal intraoperative ligament releases to balance the TKA and; • produce satisfactory improvements in functional scores at early follow-up.
curve of this technique. All patients received a cruciate-retaining, fixed bearing implant (Triathlon, Stryker, MI, US). The approach was an anterolateral skin incision [29] and medial parapatellar arthrotomy in all cases, without tourniquet. Regardless of preoperative deformity, only the deep MCL was released routinely. The patella was subluxed laterally. Kinematic alignment in the coronal plane was achieved using optical computer navigation (Orthomap ASM, Stryker, Michigan). The goal of the procedure was to resurface the knee according to each patient’s normal anatomy and therefore maintain the femoral flexion axis. Distal femoral and proximal tibial cuts were adjusted to ensure a 9 mm resection on the intact femoral condyle and tibial plateau, representing the TKA implant thickness. Cartilage and bone loss on the distal femoral condyle and tibial plateau was assessed by comparison with intact areas. On the worn side, fully exposed subchondral bone was considered to represent 3 mm of cartilage loss [30]. The coronal resection angles were then adjusted to compensate for the loss. For example, in a varus knee with full cartilage loss on the medial condyle and intact lateral side, medial resection would have been 6 mm and 9 mm laterally thus recreating the patient’s native joint orientation. When partial thickness wear was present, we had to estimate the thickness loss at 1 or 2 mm and adjust the resection accordingly. In all cases, preoperative planning was performed on long films and angles were compared with intraoperative measurements to rule out gross miscalibration of the navigation equipment, (which did not occur) and the final decisions were made on the intraoperative findings alone. Resections were modified from patient anatomy only if the measured angles fell outside a pre-defined “safe range” of either a combined coronal orientation within ± 3 degrees of neutral and/or independent femoral or tibial cuts within ± 5 degrees. An example tibial resection is shown in Figs. 1 and 2. Resection accuracy was confirmed by caliper measurements (Fig. 3). A similar procedure was followed for distal femoral resection. The remainder of the procedure was completed using standard TKA instrumentation. To resurface the posterior condyles, a posterior referencing guide was set to neutral rotation, thus resecting only the implant thickness of the posterior condyles and matching each patient’s native femoral rotation. Tibial component rotation was set relative to the trial femoral component with the knee in extension. Pre- and postoperative measurements of coronal orientation were taken using long-leg standing radiographs using the hipknee-ankle (HKA) angle, the lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA). The LDFA is the angle formed by the distal extent of the femur or femoral TKA component and the mechanical axis of the femur. The MPTA is the angle formed
2. Methods Our scientific and ethical committees approved the study and patient consent was obtained. One surgeon (PAV) performed all the operations. All patients presenting with degenerative arthritis of the knee and considered suitable for primary TKA were considered for inclusion. During this period, no other technique for TKA was used regardless of preoperative alignment, range of motion or the presence of fixed deformity. The only exclusion criteria was preoperative deformity or ligamentous incompetence that necessitated a higher level of constraint. The first 100 consecutive kinematic TKAs (95 patients, 5 bilateral procedures) with this technique were identified from our database. Patient demographics are shown in Table 1. This included all patients in the learning Table 1 Cohort demographics. M:F (%) BMI (Mean, Range, SD) Age (Mean, Range, SD)
32:63 (34%) 31 (19–47) 6 68 (38–89) 11
Fig. 1. Intraoperative photograph of the proximal tibia. The forceps tip is on the medial side, where there is full-thickness wear of the cartilage. Human knee cartilage thickness is between 2–3 mm [30]. To recreate the anatomical joint line, the resection therefore needs to be 2–3 mm less medially.
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Fig. 2. Comparative resections for the proximal tibia for mechanical and kinematic cuts.
3. Results
Fig. 3. Caliper measurement of proximal tibial resection after kinematic cuts. The calipers are on the lateral plateau.
by the mechanical axis of the tibia and the joint line or tibial base plate. Two evaluators (JH and MB) performed the measurements as described by previous authors [1,7,23]. Operative records were reviewed to establish the need for ligament release. Clinical scoring using WOMAC and KOOS scales was performed in the outpatient clinic. 2.1. Statistical analysis All calculations were performed using Prism V6.0 (Graphpad Software, US). Pre- and postoperative paired categorical data was compared using McNemar’s test (M:F ratio, number of outliers). Continuous data was tested for normality using the D’AgostinoPearson omnibus test and paired comparisons were performed using Student’s T-test (pre- and post-op LDFA, WOMAC and KOOS scores) or the Wilcoxon signed rank test (Age, BMI, pre- and post-op MPTA, pre- and post-op HKA).
The mean follow up was 2.4 years (range 1.0–3.7, SD 0.8). The pre- and postoperative measurements are shown in Table 2; valgus measurements are positive, varus measurements are negative. Fig. 4 shows the distribution of measurements for the LDFA and the MPTA. The paired comparison of these two angles are surrogates for recreation of native anatomy, unlike the HKA which preoperatively will reflect deformity due to cartilage loss. Pre-op, 15 knees had a LDFA of > 5◦ varus or valgus versus 4 post-op (P = 0.01). All these 4 post-op LDFAs outliers were in valgus at a mean of 5.3◦ (range 5.1–5.7). For the MPTA, 20 knees were in > 5◦ varus or valgus pre-op versus 12 post-op (P = 0.14). All these 12 post-op MPTAs outliers were in varus at a mean of 5.8◦ (range 5.2–6.8). The mean overall combined coronal orientation (HKA) was 0.5◦ varus (range −7.4 to 6.3, SD 2.3). Twelve knees were outliers regarding HKA, three in valgus (mean 3.5◦ , 3.2–3.9) and nine in varus (mean 3.8◦ , 3.2–4.8). We should know if these outliers correspond to pre-op marked deformity. The preoperative deformity as measured by the HKA was not significantly different between the outliers (mean 5.1◦ varus) and the non-outlier cases (mean 4.5◦ varus, P = 0.30). The differences for each individual knee from pre- to post-op are shown in Fig. 5. Only five knees (5%) required additional ligament release, four with valgus OA and one with varus OA. In these 5 knees, the patient’s anatomy felt outside our “safe range” of either a combined coronal orientation within ± 3 degrees of neutral and/or independent femoral or tibial cuts within ± 5 degrees. This may explain the need for additional ligament release. Two valgus knees (2%) required lateral retinacular release to allow satisfactory patellar tracking. The mean WOMAC score improved from 49.4 (29.0–85.0, SD 12.8) to 24.7 (0.0–73.0, SD 16.5) (P < 0.001). All KOOS scores were significantly improved (P < 0.001); pain from 38.5 (11.1–72.2, SD
Table 2 Pre- and postoperative measures of coronal alignment. Preoperative
HKA LDFA MPTA
Postoperative
P-value
Mean
Range
SD
Mean
Range
SD
−4.6 2.1 −3.0
−15.5–11.6 −3.7–9.2 −10.2–10.6
5.9 2.5 3.2
−0.5 1.8 −2.4
−7.4–6.3 −4.2–5.7 −6.8–4.0
2.3 2.0 2.2
HKA: hip-knee-ankle; LDFA: lateral distal femoral angle; MPTA: medial proximal tibial angle.
< 0.001 0.41 0.03
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Fig. 4. Histogram distribution of pre and postoperative LDFA and MPTA. The shaded area indicates the safe zone.
17.0) to 74.6 (22.0–100, SD 18.8), symptom from 39.4 (10.7–67.9, SD 12.6) to 54.8 (18.0–100, SD 26.7), ADL from 41.2 (0–86.8, SD 18.7) to 76 (25.0–100, SD 19.3), sport from 14.2 (0–100, SD 22.7) to 46.4 (0–100, SD 30.6) and quality of life from 24.1 (0–62.5, SD 18.2) to 71.9 (19–100, SD 23.1). 4. Discussion TKA outcomes have not yet reached the consistent high levels seen with total hip arthroplasty [10]. Kinematic alignment may be one solution improving patient satisfaction and function. This study evaluates a novel method using computer navigation to perform kinematic TKA and preserving patient knee anatomy within a defined threshold. Our hypotheses for the study were that kinematic alignment using navigation would: • reproduce patient anatomy as measured on comparative pre- and postoperative radiographs, and require minimal intraoperative ligament releases to balance the TKA and; • produce satisfactory improvements in functional scores at early follow-up. The results demonstrate that the technique is reproducible; it permits recreation of native anatomy within a certain range, whilst allowing for corrections when desired. The technique also has the advantage of allowing the surgeon to know the exact orientation of bony resection without the need for the additional imaging, planning and cost associated with PSI. The use of navigation has the potential for increasing operative time and costs, the latter mainly from additional training and equipment expenditure [31]. However, as this technique navigates only the coronal cuts, in a hospital setting where surgeons and
staff have considerable experience with navigation equipment, we believe this effect is minimised. Although clinical benefit remains unproven in mechanical TKA, navigation has been shown to be an accurate technique for prosthesis alignment, reducing outliers for the targeted orientation [32,33]. In terms of the alignment, there was a significant difference between pre and postoperative HKA limb alignment (4.6 to 0.5 varus, P < 0.001, Fig. 5), which is to be expected due to the effect of restoring cartilage and bone loss. Postoperatively, only 12 knees had a combined coronal orientation outside the safe range of ± 3 degrees, three in valgus (mean 3.5◦ , 3.2–3.9) and nine in varus (mean 3.8◦ , 3.2–4.8). Outliers from our safe range probably occurred as a result of slight imprecision in the navigation system, or small variations during bone cuts or implant cementation. On the femoral side, the comparative data suggests we were able to recreate the distal femoral anatomy, an important step in kinematic alignment to maintain the anatomic femoral flexion axis. Maintaining this axis is a key feature of kinematic TKR; this is why ideally no additional rotation is given to the femoral implant. However, a number of femora required a small correction to bring the measurements into our safe range; 15 knees had a pre-op LDFA of > 5 deg, reduced to only 4 knees post-op (P = 0.01). A total of 2/4 (50%) in this latter category were under corrected from pre-op. Most of the significant corrections were performed on the tibial side. The preoperative MPTA range was from 10.6 valgus to 10.2 varus, reduced to 4.0 valgus to 6.8 varus postop. Although not statistically significant, fewer cases were outside of safe range postoperatively, with 12 cases at greater than ± 5◦ post-op versus 20 cases pre-op (P = 0.14). A total of 6/12 (50%) of the cases with post-op values outside the safe range were under corrected from pre-op. Overall, individual changes in alignment angles, represented in Fig. 5, demonstrate that the described technique reliably brought these measurements to within the desired
Fig. 5. Individual corrections for HKA, LDFA and MPTA. The shaded area indicates the safe zone.
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limits. With corrections, the post-op measured angles and overall alignment in this study showed ranges and standard deviations similar to both normal anatomy in asymptomatic volunteers as well as to other reports of component orientation after kinematic TKA [13,23,24]. This probably results from the fact that the majority of patients’ normal anatomy, certainly in this cohort, falls within the self-imposed limits of this technique. Only 5% of our cohort required ligament release for a balanced implantation. Other series of kinematic TKA have recorded the need for ligament release [24,28], the valgus knee remains problematic; the need for further balancing is not completely eliminated in these patients with kinematic alignment. In another similar size series, Howell et al. report a need for release of lateral structures in 17% of their patients [28]. This factor is affected by nuances in technique; the study by Howell et al. also incorporates modified tibial resection for coronal balance, and this study has self-imposed alignment boundaries. Both of these will have subtle effects on the need for ligament balancing. Our study has limitations. Despite its frequent use in published literature, a single coronal measurement is not a completely adequate way of assessing alignment even with standardised radiography. The numbers are relatively small, and therefore cannot be completely representative of anatomical variation in TKA patients. Although there were no early failures in this cohort, we cannot make inferences about the effect of this technique on long-term function or survivorship. At the time of writing, published comparisons between the two techniques are few, with only one randomised study in the literature. Dossett et al. found that despite the expected variations in femoral and tibial component obliquity, both kinematic and mechanically aligned TKAs showed similar results in overall alignment at the earlier follow-up point [24], although better outcome scores were seen in the kinematic group at two years [34]. Other case series have shown good functional outcomes for kinematic TKA [13,28], but there is limited long-term data; the question of whether it can provide better clinical function and satisfaction while maintaining the long term survivorship offered by classical mechanically aligned TKA is currently unanswered. Long term cohort studies, radio steriometric analysis studies, and further randomised trials are warranted. In conclusion, this study demonstrates that using computer navigation allows the operating surgeon to perform kinematic TKA by restoring knee anatomy in most cases and partially correcting some extreme anatomy that might be unsuitable for recreation with TKA. Further studies should be undertaken to determine the safe orientation and alignment boundaries associated with TKAs implanted with differing alignment philosophies. Funding No funding was received for this study. Disclosure of interest The authors declare that they have no competing interest. References [1] Cherian JJ, Kapadia BH, Banerjee S, Jauregui JJ, Issa K, Mont MA. Mechanical, anatomical, and kinematic axis in TKA: concepts and practical applications. Curr Rev Musculoskelet Med 2014;7:89–95, http://dx.doi.org/10.1007/ s12178-014-9218-y. [2] Rodricks DJ, Patil S, Pulido P, Colwell CW. Press-fit condylar design total knee arthroplasty. Fourteen to seventeen-year follow-up. J Bone Joint Surg Am 2007;89:89–95, http://dx.doi.org/10.2106/JBJS.E.00492.
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