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Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients
THEKNE-02520; No of Pages 7 The Knee xxx (2017) xxx–xxx
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The Knee
Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients Lena Alm, Matthias Krause, Carolin Mull, Karl-Heinz Frosch ⁎, Ralph Akoto Department of Trauma and Reconstructive Surgery with Division of Knee and Shoulder Surgery, Sports Traumatology, Asklepios Clinic St. Georg, Hamburg, Germany
a r t i c l e
i n f o
Article history: Received 31 January 2017 Received in revised form 26 July 2017 Accepted 10 August 2017 Available online xxxx Keywords: Patella dislocation MPFL Children and adolescents Modified adductor sling
a b s t r a c t Background: Due to open femoral physis the therapy of patellar instability in skeletally immature patients is challenging. We developed a modified surgical technique of the ‘Adductor-SlingApproach’ by Sillanpää. The purpose of this study was to evaluate the clinical outcome of the operative technique and to analyse the reasons for failure. Methods: Thirty ‘modified adductor sling’ reconstructions in 28 patients were included in the study. From 2010 to 2016 modified adductor sling reconstruction was performed by looping the gracilis or semitendinosus tendon around the adductor magnus tendon and attaching it at the medial facet of the patella. Clinical outcome was retrospectively evaluated at a mean follow up of 25.6 months (range 12–43). The evaluation also included subjective International Knee Documentation Committee (IKDC), Lysholm Score, Kujala Score and Tegner Activity Score. Results: The average age at the time of operation was 15.10 years (range 11–17). Eighty-seven percent of the patients, who underwent the modified adductor sling technique, gained a stable patella and excellent results in postoperative scores. Recurrent dislocation occurred in four of 30 cases (13%). Analysis showed that possible reasons for failure of the tendon graft could be maltracking of the patella due to patella alta, trochlear dysplasia or an elevated tibial tuberosity to trochlear groove distance. Conclusion: The modified adductor sling technique for MPFL reconstruction in children and adolescents showed elevated redislocation rates. Only in absence of additional patellofemoral maltracking, caused by elevated tibial tubercle to trochlear groove distance (N15 mm), patella alta or especially severe trochlear dysplasia, the modified adductor sling technique could be recommended. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Patellar dislocation in children and adolescents (10–17 years) occurs in 29–43/100,000 and is 10-times higher compared to adults (2.3–7.0/100,000) [1]. While habitual lateral dislocation is more common and often triggered by so-called trivial trauma when climbing stairs, running or standing up from a chair, traumatic patellar dislocation is rather unusual and occurs in less than 3% of cases [2]. In 78–94% of patellar dislocations the medial patellofemoral ligament (MPFL) ruptures [3–5]. As the most important passive stabilizer of the patella, the MPFL can cause recurrent patellar dislocations or chronic instability in 71% of children and in 30% of adults when it is torn or insufficiently healed [6,7].
⁎ Corresponding author at: Department of Trauma and Reconstructive Surgery with Division of Knee and Shoulder Surgery, Sports Traumatology, Asklepios Clinic St. Georg, Lohmühlenstraße 5, 20099 Hamburg, Germany. E-mail address: [email protected] (K.-H. Frosch).
http://dx.doi.org/10.1016/j.knee.2017.08.051 0968-0160/© 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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A common procedure in adult MPFL reconstructions is to attach autologous tendons via bony fixation at the medial side of the femur to restore the MPFL [8,9]. Promising results with no recurrent dislocation and good to excellent postoperative scores are described in retrospective studies [10–13]. Several techniques have already been published using bony fixation for MPFL reconstruction in children and adolescents [8]. Femoral fixation is 6.4 mm (2.9–8.5 mm) distal to the physis [9]. There is potential risk of injuring the physis and causing growth disturbance. Long-term studies for MPFL reconstruction with bony fixation in skeletally immature patients do not exist to date. However, a study that pointed out the risk of transphyseal drilling in skeletally immature patients with ACL injuries, showed a leg-shortening in 24% and valgus deviation in 82% of patients after surgery [14]. We developed a surgical technique, a modified form of the ‘Adductor-Sling-Approach’ by Sillanpää et al. which stabilizes the patella and provides no injury to the femoral growth plate [1,15]. Sillanpää et al. passed one end of a free semitendinosus/gracilis graft through the patella and looped the other end around the adductor magnus tendon. Then they stitched both parts of the graft together. This technique causes no damage to the physis and only little soft tissue injury. Studies examining postoperative results do not exist [15]. To lower possible postoperative risks, we modified this technique. Transverse patellar drilling can cause patellar fracture, intra- and postoperatively [16,17]. To fix the graft at the patella, we used suture anchors at the medial side of the patella to reduce the risk of patellar fractures. Also, we left the distal insertion of the tendon intact to lower postoperative morbidity at the distal graft removal site and also to provide a dynamic stabilization of the patella [18] (Figure 1). A large number of surgical procedures have been developed in attempts to treat patellofemoral instability in children and adolescents but a standardized concept for surgical therapy does not exist [10,15,19,20]. The purpose of this study was to examine the clinical outcome for patients operated on by the ‘modified adductor sling technique’. Also in cases of recurrent dislocation, we analysed possible reasons for failure. 2. Materials and methods 2.1. Patient population In a retrospective study, between 2010 and 2016, patients with multiple dislocations of the patella (N 1 dislocation) and patients with first-time dislocation combined with concomitant injuries like appearance of osteochondral flakes and with open physis were included in the study. Thirty-five patients were eligible for the study, seven patients were subsequently excluded: five were unable to present for a follow-up examination and two were unwilling to participate in the study. Subsequently, 28 patients with 30 surgical interventions were included in the study, 17 girls and 11 boys (range 11–17 years). The study design was approved by the local ethics committee (#2953). 2.2. Surgical technique First, arthroscopy was carried out for cartilage and ligament evaluation as well as visualization of the patellofemoral tracking during flexion and extension. Then, the semitendinosus or gracilis tendon was harvested, the distal insertion of the tendon was left intact. At the medial side of the distal femur, a small incision of two centimetres was made and the distal segment of the adductor magnus was exposed. The harvested tendon was shuttled to this incision and passed around the distal segment of the adductor magnus tendon from posterior to anterior. Another two-centimetre incision was made at the medial facette of the patella and a suture anchor was placed. Afterwards the free end of the tendon was fixed to the medial facette of the patella at 30° of knee flexion. 2.3. Postoperative care After surgery all patients were treated by standard protocol: partial weight bearing with 20 kg for 4 weeks, with limitation for range of motion up to 90° of flexion. Then weight bearing was subsequently increased by 10 kg each week until the patient achieved full weight bearing after 6 weeks. 2.4. Clinical testing protocol Age, affected side, sex, date of surgery and surgical history were obtained from medical records. Also, recurrent dislocations, cause of first dislocation before surgery, number of frank patellar dislocation episodes before surgery and complaints of the mutual knee were collected. Preoperative assessment comprised physical examination, plain radiographs in three planes (coronal, sagittal, axial) and magnetic resonance imaging of the injured knee in order to assess patellofemoral dysplasia using the Déjour Classification [21], while patella height was measured with the Insall–Salvati ratio [22]. Tibial tuberosity to trochlear groove (TTTG) distance was measured according to previously described methods [23] and maltracking of the patella was evaluated and defined as previously published [24]. After surgery postoperative radiographs were performed in sagittal and coronal views (Figure 2). Follow up examination was performed on average at 25.6 months (range 12–43) including clinical examination and acquisition of symptoms. Also range of motion was evaluated and stated to be reduced when knee flexion was less than 130°. Postoperative functional outcome was assessed with use of scoring systems by Kujala et al. [25], Lysholm et al. [26] and subjective International Knee Documentation Committee (IKDC) [27]. Excellent results were determined to be in a range from 91 to 100 points, good results from 81 to 90, and fair or poor results were less than 80 points. Physical activity level was measured by the scale of Tegner [28]. We used visual analogous scale (VAS) for the quantification of subjective pain [29]. Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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Figure 1. Schematic illustration of the modified adductor sling technique. The semitendinosus/gracilis tendon is looped around the adductor magnus tendon and fixed at the medial side of the patella with a suture anchor.
2.5. Statistical analysis Descriptive statistics are given as median and range. Calculation was based on two groups; patients were postoperatively divided into groups of stable patella and failure (redislocation after surgery). Mean differences between treatment success at follow up and treatment failure were calculated with unpaired Student's t-test for parametric and Kruskal–Wallis test for non-parametric parameters. Categorical parameters were compared using Chi-Squared test. Treatment accepted was defined as a persistent subjective instability or patella redislocation after surgery. Statistical analysis was performed using IBM®SPSS®Statistics Version 21. A Pvalue less than 0.5 was considered significant. Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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Figure 2. (a) Preoperative radiograph in anterior–posterior view showing lateralized patella after multiple dislocations. (b) Postoperative radiograph in anterior– posterior view showing a performed modified adductor sling technique with fixed suture anchor at the medial facette of the patella.
3. Results 3.1. Descriptive results Until the last follow up, in 87% (26 of 30) of the cases no instability could be detected. Redislocation occurred in four out of 30 patients. Each of these four patients showed at least two of the redislocation risk factors. Three of the patients showed an elevated TTTG (N15 mm) or severe trochlear dysplasia (type B–D according to Déjour), two had patella alta (Insall–Salvati N 1.2) and one valgus malalignment. Dislocation happened on average 6.25 (range 5–10) months after surgery. The mean age at time of surgery was 15.1 (range 11–17) years, while at time of first-time dislocation patients were on average 13.84 (range 10–16) years old. The main reason for first-time dislocation proved to be a habitual course of events. On average, eight dislocations (range 2–40) were observed prior surgery, while there was no difference between both study groups. All patients showed a normal range of motion without any signs of hyperextension of the knee and the passive patellar glide test was negative. Also, patients with stable patella demonstrated a tendency to a lower TTTG (P N 0.05) or patella height (P b 0.05) and significantly less frequent trochlear dysplasia compared to patients with failed surgical therapy (P = 0.042, Table 1). 3.2. Postoperative results Patients with a stable patella achieved excellent results of 92 points in IKDC (P b 0.001), 94 points in Kujala Score (P = 0.003) and 92 points in Lysholm Score (P = 0.002), unlike patients with secondary dislocation whose results were significantly poorer. All four patients who experienced recurrent dislocation after surgery demonstrated maltracking compared to patients with a stable patella (P = 0.003). None of the patients had a knee infection, pain at the medial facette of the patella or reduced range of motion (Table 2). 4. Discussion Reconstruction of the MPFL plays a key role in the surgical therapy of recurrent patellar dislocation. Various techniques have already been described for surgical methods in patellar instability of the skeletally immature patient but standard procedures are still missing. In skeletally immature patients, a risk of damaging the open physis remains. The most important finding of this study is that 87% of the patients who were operated on using the modified adductor sling technique gain a stable patella and excellent results in postoperative scores. However, it is worth mentioning that in four cases recurrent dislocation occurred (13%). The reason for the use of the modified adductor sling technique in children and adolescents is to avoid injuring the open growth plate because no drilling in the immature bone is needed. Thus, it does not pose any risk of future growth disturbances. In line with other studies on epiphyseal sparing femoral soft tissue fixation techniques, patients treated with the modified adductor sling technique showed excellent results of over 90 points in postoperative scores like IKDC or Lysholm [30,32]. Nevertheless, most Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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Table 1 Descriptive results.
Total patients Total knees Number of female patients Right knee involved Dislocation of the other knee Cause of dislocation (atraumatic) Age at first dislocation (years) Number of preoperative dislocations Age at surgery (years) Time to recurrent dislocation Final follow up (months) TTTG (mm) Mean Insall–Salvati ratio No trochlea dysplasia Trochlea dysplasia Déjour classification (A) Trochlea dysplasia Déjour classification (B) Trochlea dysplasia Déjour classification (C)
Median/range overall
Median/range stable patella
Median/range redislocation after surgery
P⁎
28 30 17/28 13/30 11/30 28/30 13.84 (10–16) 8.0 (2–40) 15.10 (11–17) 6.25 (5–10) 25.56 (12–43) 15.72 (7–25) 1.48 (1–2) 16/30 3/30 8/30 3/30
24 26 13/24 11/26 10/26 24/26 13.95 (10–16) 8.14 (1–40) 15.23 (11–17) —
4 4 4/4 2/4 1/4 4/4 13.0 (12–14) 7.0 (2–15) 14.25 (13–17) 6.25 (5–10) 26.33 (15–33) 16.5 (13–20) 1.5 (1–2) 1/4 0 1/4 2/4
— — n.s. n.s. n.s. n.s. n.s.
25.27 (12–43) 15.65 (7–25) 1.48 (1–2) 15/26 3/26 7/26 1/26
n.s. n.s. — n.s. n.s. n.s. 0.042
n.s., not significant; TTTG, tibial tuberosity to trochlear groove distance. ⁎ Significant differences were evaluated between the groups of stable patella and redislocation after surgery.
femoral soft tissue fixation techniques, as well as our results, showed higher redislocation rates than femoral screw fixation techniques [19,31,33]. Lind et al. presented an epiphyseal sparing femoral soft tissue fixation technique that used the adductor magnus tendon insertion to fix their transplant [30]. They analysed the outcome of 24 MPFL reconstructions in 20 operated children, where a released gracilis tendon was looped around the adductor magnus tendon insertion and then fixed at the proximal medial patellar edge. The postoperative Kujala score was 81. Recurrent dislocation was seen in 20% of the patients within the first postoperative year; 25% of the patients even suffered from subluxation [30]. Letts et al., analysing 26 knees in 22 children and using a semitendinosus tenodesis to the adductor tendon, reported a 12% redislocation rate after three years of follow up [31]. Abouelsoud et al. presented a reconstruction without hardware fixation using a harvested quadriceps tendon. The tendon was fixed with a suture at two points: through bone and strong periosteum at the medial epicondyle and at the adductor magnus tendon. No redislocation occurred at a follow up of 29 months. Cases with severe trochlear dysplasia were excluded from the study and patient population was 16 in total [32]. The better outcome in comparison to the other femoral soft tissue fixation techniques as well as to our results considering stable patella after surgery was probably due to exclusion of skeletally abnormal knees [32]. In contrast to the epiphyseal sparing femoral soft tissue fixation techniques, Nelitz et al. used a free looped gracilis graft with a bioresorbable screw fixation to the medial side of the femur [19]. Including 21 children and adolescents with 2.8 years follow up,
Table 2 Postoperative results.
Subjective IKDC postoperative Lysholm score postoperative Kujala postoperative Tegner activity level postoperative VAS postoperatively Positive maltracking postoperative Sign of inflammation Reduced postoperative ROM (b130°) Pain at the medial facette of the patella
Median/range overall
Median/range stable patella
Median/range redislocation after surgery
P⁎
87.10 (29–100) 88.80 (53–100) 91.12 (57–100) 6.04 (3–9) 0.57 (0–4) 11/30 0/30 0/30 0/30
91.83 (58–100) 92.05 (58–100) 93.86 (57–100) 6.41 (5–9) 0.58 (0–4) 7/26 0/26 0/26 0/26
52.43 (29–76) 65.00 (53–85) 71.00 (58–90) 3.33 (3–4) 0.5 (0–1) 4/4 0/4 0/4 0/4
b0.001 0.002 0.003 b0.001 n.s. 0.003 — — —
n.s., not significant; IKDC, International Knee Documentation Committee; ROM, range of motion; VAS, visual analogous scale. ⁎ Significant differences were evaluated between the group of stable patella and failed surgery.
Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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they used bony fixation in children and adolescents which was 6.4 mm (2.9–8.5 mm) distal to the physis. Interestingly, 20 out of 21 patients had severe trochlea dysplasia (Déjour B–D) [13,19]. Postoperative mean Kujala score was 92.8 and no recurrent patella dislocation occurred at follow up of 2.8 years [19]. This study showed excellent results, especially considering the rate of recurrent dislocations; also, no growth failure occurred at the time of follow up. However, placing drill holes in skeletally immature bones with open physis is still controversial. So far there have not been any studies examining long-term follow up after MPFL reconstruction using bony fixation. A long-term growth disturbance remains unclear. Other studies in paediatric surgery show a high rate of growth disturbance when damaging the growth plate. In a study analysing transphyseal drilling in skeletally immature patients with anterior cruciate ligament injury, more than 10 mm femoral length shortening of the operated leg was detected in 24% of the patients. The mean length shortening was 3.5 mm and 82% of the patients showed valgus deviation of two degrees on the operated leg [14]. Interestingly, in our study population, three of four patients who suffered a redislocation after MPFL reconstruction had trochlear dysplasia; three had an elevated TTTG distance (N15 mm) and two had patella alta with an Insall–Salvati N 1.2 and one had valgus malalignment. All of these patients showed at least two of the redislocation predicting factors. An elevated TTTG distance (N 15 mm) as well as patella alta have been identified as significant risk factors for patella redislocation after conservative treatment of first time dislocation in children [34,35]. In line with our results Steensen et al. showed that patella alta frequently co-exists with trochlear dysplasia [36]. However, Nelitz et al. performed an analysis on 37 children and adolescents with recurrent patellar instability after unsuccessful operation. Although TTTG distance and patella alta were not detected as a reason for failure, trochlear dysplasia was stated to be a major risk factor for recurrent dislocation after surgical reconstruction [37]. Due to high redislocation rates observed for MPFL reconstruction techniques with femoral soft tissue fixation, which was confirmed by our results, we see limited indication for these techniques. Only in the absence of additional risk factors such as elevated TTTG (N15 mm), patella alta, valgus or torsional malalignment, the modified adductor sling technique could be recommended as a therapeutic option for recurrent patella instability in children. Especially in cases of severe trochlea dysplasia (Déjour B–D) femoral soft tissue reconstruction techniques could not be recommended. When additional risk factors such as severe trochlear dysplasia (Déjour B–D) occur, low redislocation rates could be achieved with femoral screw fixation techniques taking into account the risk of injuring the femoral growth plate [37,33]. A limitation of the study was that no preoperative randomization was performed due to the retrospective study design. Our selection was made at the time of operation and we described the outcome postoperatively. Furthermore, follow up was only 12 months in one case. This could alter the results as recurrent dislocation can occur later than that time. Also, this study was based on a relatively small number of 30 procedures, so we cannot be certain whether this approach is superior to other surgical techniques. Another limitation is that the group of patients with failed surgery encompasses only four patients. It was not possible to perform multivariate analysis to identify interactions of different risk factors. Hence, this technique proved to be useful at short-term follow up. Also, we did not collect data regarding scores at the time before surgery; a comparison between pre- and postoperative condition of the patients could not be made. Further investigations in terms of long-term results of the modified adductor sling technique should be evaluated in future studies. 5. Conclusions The modified adductor sling technique for MPFL reconstruction in children and adolescents showed elevated redislocation rates. Only in the absence of additional patellofemoral maltracking, caused by elevated TTTG (N15 mm), patella alta or especially severe trochlear dysplasia, the modified adductor sling technique could be recommended. Acknowledgements Each author certifies that no financial support was received for this study. The study was funded by Asklepios Kliniken Hamburg GmbH (#2953). 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Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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The Knee
Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients Lena Alm, Matthias Krause, Carolin Mull, Karl-Heinz Frosch ⁎, Ralph Akoto Department of Trauma and Reconstructive Surgery with Division of Knee and Shoulder Surgery, Sports Traumatology, Asklepios Clinic St. Georg, Hamburg, Germany
a r t i c l e
i n f o
Article history: Received 31 January 2017 Received in revised form 26 July 2017 Accepted 10 August 2017 Available online xxxx Keywords: Patella dislocation MPFL Children and adolescents Modified adductor sling
a b s t r a c t Background: Due to open femoral physis the therapy of patellar instability in skeletally immature patients is challenging. We developed a modified surgical technique of the ‘Adductor-SlingApproach’ by Sillanpää. The purpose of this study was to evaluate the clinical outcome of the operative technique and to analyse the reasons for failure. Methods: Thirty ‘modified adductor sling’ reconstructions in 28 patients were included in the study. From 2010 to 2016 modified adductor sling reconstruction was performed by looping the gracilis or semitendinosus tendon around the adductor magnus tendon and attaching it at the medial facet of the patella. Clinical outcome was retrospectively evaluated at a mean follow up of 25.6 months (range 12–43). The evaluation also included subjective International Knee Documentation Committee (IKDC), Lysholm Score, Kujala Score and Tegner Activity Score. Results: The average age at the time of operation was 15.10 years (range 11–17). Eighty-seven percent of the patients, who underwent the modified adductor sling technique, gained a stable patella and excellent results in postoperative scores. Recurrent dislocation occurred in four of 30 cases (13%). Analysis showed that possible reasons for failure of the tendon graft could be maltracking of the patella due to patella alta, trochlear dysplasia or an elevated tibial tuberosity to trochlear groove distance. Conclusion: The modified adductor sling technique for MPFL reconstruction in children and adolescents showed elevated redislocation rates. Only in absence of additional patellofemoral maltracking, caused by elevated tibial tubercle to trochlear groove distance (N15 mm), patella alta or especially severe trochlear dysplasia, the modified adductor sling technique could be recommended. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Patellar dislocation in children and adolescents (10–17 years) occurs in 29–43/100,000 and is 10-times higher compared to adults (2.3–7.0/100,000) [1]. While habitual lateral dislocation is more common and often triggered by so-called trivial trauma when climbing stairs, running or standing up from a chair, traumatic patellar dislocation is rather unusual and occurs in less than 3% of cases [2]. In 78–94% of patellar dislocations the medial patellofemoral ligament (MPFL) ruptures [3–5]. As the most important passive stabilizer of the patella, the MPFL can cause recurrent patellar dislocations or chronic instability in 71% of children and in 30% of adults when it is torn or insufficiently healed [6,7].
⁎ Corresponding author at: Department of Trauma and Reconstructive Surgery with Division of Knee and Shoulder Surgery, Sports Traumatology, Asklepios Clinic St. Georg, Lohmühlenstraße 5, 20099 Hamburg, Germany. E-mail address: [email protected] (K.-H. Frosch).
http://dx.doi.org/10.1016/j.knee.2017.08.051 0968-0160/© 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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A common procedure in adult MPFL reconstructions is to attach autologous tendons via bony fixation at the medial side of the femur to restore the MPFL [8,9]. Promising results with no recurrent dislocation and good to excellent postoperative scores are described in retrospective studies [10–13]. Several techniques have already been published using bony fixation for MPFL reconstruction in children and adolescents [8]. Femoral fixation is 6.4 mm (2.9–8.5 mm) distal to the physis [9]. There is potential risk of injuring the physis and causing growth disturbance. Long-term studies for MPFL reconstruction with bony fixation in skeletally immature patients do not exist to date. However, a study that pointed out the risk of transphyseal drilling in skeletally immature patients with ACL injuries, showed a leg-shortening in 24% and valgus deviation in 82% of patients after surgery [14]. We developed a surgical technique, a modified form of the ‘Adductor-Sling-Approach’ by Sillanpää et al. which stabilizes the patella and provides no injury to the femoral growth plate [1,15]. Sillanpää et al. passed one end of a free semitendinosus/gracilis graft through the patella and looped the other end around the adductor magnus tendon. Then they stitched both parts of the graft together. This technique causes no damage to the physis and only little soft tissue injury. Studies examining postoperative results do not exist [15]. To lower possible postoperative risks, we modified this technique. Transverse patellar drilling can cause patellar fracture, intra- and postoperatively [16,17]. To fix the graft at the patella, we used suture anchors at the medial side of the patella to reduce the risk of patellar fractures. Also, we left the distal insertion of the tendon intact to lower postoperative morbidity at the distal graft removal site and also to provide a dynamic stabilization of the patella [18] (Figure 1). A large number of surgical procedures have been developed in attempts to treat patellofemoral instability in children and adolescents but a standardized concept for surgical therapy does not exist [10,15,19,20]. The purpose of this study was to examine the clinical outcome for patients operated on by the ‘modified adductor sling technique’. Also in cases of recurrent dislocation, we analysed possible reasons for failure. 2. Materials and methods 2.1. Patient population In a retrospective study, between 2010 and 2016, patients with multiple dislocations of the patella (N 1 dislocation) and patients with first-time dislocation combined with concomitant injuries like appearance of osteochondral flakes and with open physis were included in the study. Thirty-five patients were eligible for the study, seven patients were subsequently excluded: five were unable to present for a follow-up examination and two were unwilling to participate in the study. Subsequently, 28 patients with 30 surgical interventions were included in the study, 17 girls and 11 boys (range 11–17 years). The study design was approved by the local ethics committee (#2953). 2.2. Surgical technique First, arthroscopy was carried out for cartilage and ligament evaluation as well as visualization of the patellofemoral tracking during flexion and extension. Then, the semitendinosus or gracilis tendon was harvested, the distal insertion of the tendon was left intact. At the medial side of the distal femur, a small incision of two centimetres was made and the distal segment of the adductor magnus was exposed. The harvested tendon was shuttled to this incision and passed around the distal segment of the adductor magnus tendon from posterior to anterior. Another two-centimetre incision was made at the medial facette of the patella and a suture anchor was placed. Afterwards the free end of the tendon was fixed to the medial facette of the patella at 30° of knee flexion. 2.3. Postoperative care After surgery all patients were treated by standard protocol: partial weight bearing with 20 kg for 4 weeks, with limitation for range of motion up to 90° of flexion. Then weight bearing was subsequently increased by 10 kg each week until the patient achieved full weight bearing after 6 weeks. 2.4. Clinical testing protocol Age, affected side, sex, date of surgery and surgical history were obtained from medical records. Also, recurrent dislocations, cause of first dislocation before surgery, number of frank patellar dislocation episodes before surgery and complaints of the mutual knee were collected. Preoperative assessment comprised physical examination, plain radiographs in three planes (coronal, sagittal, axial) and magnetic resonance imaging of the injured knee in order to assess patellofemoral dysplasia using the Déjour Classification [21], while patella height was measured with the Insall–Salvati ratio [22]. Tibial tuberosity to trochlear groove (TTTG) distance was measured according to previously described methods [23] and maltracking of the patella was evaluated and defined as previously published [24]. After surgery postoperative radiographs were performed in sagittal and coronal views (Figure 2). Follow up examination was performed on average at 25.6 months (range 12–43) including clinical examination and acquisition of symptoms. Also range of motion was evaluated and stated to be reduced when knee flexion was less than 130°. Postoperative functional outcome was assessed with use of scoring systems by Kujala et al. [25], Lysholm et al. [26] and subjective International Knee Documentation Committee (IKDC) [27]. Excellent results were determined to be in a range from 91 to 100 points, good results from 81 to 90, and fair or poor results were less than 80 points. Physical activity level was measured by the scale of Tegner [28]. We used visual analogous scale (VAS) for the quantification of subjective pain [29]. Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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Figure 1. Schematic illustration of the modified adductor sling technique. The semitendinosus/gracilis tendon is looped around the adductor magnus tendon and fixed at the medial side of the patella with a suture anchor.
2.5. Statistical analysis Descriptive statistics are given as median and range. Calculation was based on two groups; patients were postoperatively divided into groups of stable patella and failure (redislocation after surgery). Mean differences between treatment success at follow up and treatment failure were calculated with unpaired Student's t-test for parametric and Kruskal–Wallis test for non-parametric parameters. Categorical parameters were compared using Chi-Squared test. Treatment accepted was defined as a persistent subjective instability or patella redislocation after surgery. Statistical analysis was performed using IBM®SPSS®Statistics Version 21. A Pvalue less than 0.5 was considered significant. Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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Figure 2. (a) Preoperative radiograph in anterior–posterior view showing lateralized patella after multiple dislocations. (b) Postoperative radiograph in anterior– posterior view showing a performed modified adductor sling technique with fixed suture anchor at the medial facette of the patella.
3. Results 3.1. Descriptive results Until the last follow up, in 87% (26 of 30) of the cases no instability could be detected. Redislocation occurred in four out of 30 patients. Each of these four patients showed at least two of the redislocation risk factors. Three of the patients showed an elevated TTTG (N15 mm) or severe trochlear dysplasia (type B–D according to Déjour), two had patella alta (Insall–Salvati N 1.2) and one valgus malalignment. Dislocation happened on average 6.25 (range 5–10) months after surgery. The mean age at time of surgery was 15.1 (range 11–17) years, while at time of first-time dislocation patients were on average 13.84 (range 10–16) years old. The main reason for first-time dislocation proved to be a habitual course of events. On average, eight dislocations (range 2–40) were observed prior surgery, while there was no difference between both study groups. All patients showed a normal range of motion without any signs of hyperextension of the knee and the passive patellar glide test was negative. Also, patients with stable patella demonstrated a tendency to a lower TTTG (P N 0.05) or patella height (P b 0.05) and significantly less frequent trochlear dysplasia compared to patients with failed surgical therapy (P = 0.042, Table 1). 3.2. Postoperative results Patients with a stable patella achieved excellent results of 92 points in IKDC (P b 0.001), 94 points in Kujala Score (P = 0.003) and 92 points in Lysholm Score (P = 0.002), unlike patients with secondary dislocation whose results were significantly poorer. All four patients who experienced recurrent dislocation after surgery demonstrated maltracking compared to patients with a stable patella (P = 0.003). None of the patients had a knee infection, pain at the medial facette of the patella or reduced range of motion (Table 2). 4. Discussion Reconstruction of the MPFL plays a key role in the surgical therapy of recurrent patellar dislocation. Various techniques have already been described for surgical methods in patellar instability of the skeletally immature patient but standard procedures are still missing. In skeletally immature patients, a risk of damaging the open physis remains. The most important finding of this study is that 87% of the patients who were operated on using the modified adductor sling technique gain a stable patella and excellent results in postoperative scores. However, it is worth mentioning that in four cases recurrent dislocation occurred (13%). The reason for the use of the modified adductor sling technique in children and adolescents is to avoid injuring the open growth plate because no drilling in the immature bone is needed. Thus, it does not pose any risk of future growth disturbances. In line with other studies on epiphyseal sparing femoral soft tissue fixation techniques, patients treated with the modified adductor sling technique showed excellent results of over 90 points in postoperative scores like IKDC or Lysholm [30,32]. Nevertheless, most Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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Table 1 Descriptive results.
Total patients Total knees Number of female patients Right knee involved Dislocation of the other knee Cause of dislocation (atraumatic) Age at first dislocation (years) Number of preoperative dislocations Age at surgery (years) Time to recurrent dislocation Final follow up (months) TTTG (mm) Mean Insall–Salvati ratio No trochlea dysplasia Trochlea dysplasia Déjour classification (A) Trochlea dysplasia Déjour classification (B) Trochlea dysplasia Déjour classification (C)
Median/range overall
Median/range stable patella
Median/range redislocation after surgery
P⁎
28 30 17/28 13/30 11/30 28/30 13.84 (10–16) 8.0 (2–40) 15.10 (11–17) 6.25 (5–10) 25.56 (12–43) 15.72 (7–25) 1.48 (1–2) 16/30 3/30 8/30 3/30
24 26 13/24 11/26 10/26 24/26 13.95 (10–16) 8.14 (1–40) 15.23 (11–17) —
4 4 4/4 2/4 1/4 4/4 13.0 (12–14) 7.0 (2–15) 14.25 (13–17) 6.25 (5–10) 26.33 (15–33) 16.5 (13–20) 1.5 (1–2) 1/4 0 1/4 2/4
— — n.s. n.s. n.s. n.s. n.s.
25.27 (12–43) 15.65 (7–25) 1.48 (1–2) 15/26 3/26 7/26 1/26
n.s. n.s. — n.s. n.s. n.s. 0.042
n.s., not significant; TTTG, tibial tuberosity to trochlear groove distance. ⁎ Significant differences were evaluated between the groups of stable patella and redislocation after surgery.
femoral soft tissue fixation techniques, as well as our results, showed higher redislocation rates than femoral screw fixation techniques [19,31,33]. Lind et al. presented an epiphyseal sparing femoral soft tissue fixation technique that used the adductor magnus tendon insertion to fix their transplant [30]. They analysed the outcome of 24 MPFL reconstructions in 20 operated children, where a released gracilis tendon was looped around the adductor magnus tendon insertion and then fixed at the proximal medial patellar edge. The postoperative Kujala score was 81. Recurrent dislocation was seen in 20% of the patients within the first postoperative year; 25% of the patients even suffered from subluxation [30]. Letts et al., analysing 26 knees in 22 children and using a semitendinosus tenodesis to the adductor tendon, reported a 12% redislocation rate after three years of follow up [31]. Abouelsoud et al. presented a reconstruction without hardware fixation using a harvested quadriceps tendon. The tendon was fixed with a suture at two points: through bone and strong periosteum at the medial epicondyle and at the adductor magnus tendon. No redislocation occurred at a follow up of 29 months. Cases with severe trochlear dysplasia were excluded from the study and patient population was 16 in total [32]. The better outcome in comparison to the other femoral soft tissue fixation techniques as well as to our results considering stable patella after surgery was probably due to exclusion of skeletally abnormal knees [32]. In contrast to the epiphyseal sparing femoral soft tissue fixation techniques, Nelitz et al. used a free looped gracilis graft with a bioresorbable screw fixation to the medial side of the femur [19]. Including 21 children and adolescents with 2.8 years follow up,
Table 2 Postoperative results.
Subjective IKDC postoperative Lysholm score postoperative Kujala postoperative Tegner activity level postoperative VAS postoperatively Positive maltracking postoperative Sign of inflammation Reduced postoperative ROM (b130°) Pain at the medial facette of the patella
Median/range overall
Median/range stable patella
Median/range redislocation after surgery
P⁎
87.10 (29–100) 88.80 (53–100) 91.12 (57–100) 6.04 (3–9) 0.57 (0–4) 11/30 0/30 0/30 0/30
91.83 (58–100) 92.05 (58–100) 93.86 (57–100) 6.41 (5–9) 0.58 (0–4) 7/26 0/26 0/26 0/26
52.43 (29–76) 65.00 (53–85) 71.00 (58–90) 3.33 (3–4) 0.5 (0–1) 4/4 0/4 0/4 0/4
b0.001 0.002 0.003 b0.001 n.s. 0.003 — — —
n.s., not significant; IKDC, International Knee Documentation Committee; ROM, range of motion; VAS, visual analogous scale. ⁎ Significant differences were evaluated between the group of stable patella and failed surgery.
Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051
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they used bony fixation in children and adolescents which was 6.4 mm (2.9–8.5 mm) distal to the physis. Interestingly, 20 out of 21 patients had severe trochlea dysplasia (Déjour B–D) [13,19]. Postoperative mean Kujala score was 92.8 and no recurrent patella dislocation occurred at follow up of 2.8 years [19]. This study showed excellent results, especially considering the rate of recurrent dislocations; also, no growth failure occurred at the time of follow up. However, placing drill holes in skeletally immature bones with open physis is still controversial. So far there have not been any studies examining long-term follow up after MPFL reconstruction using bony fixation. A long-term growth disturbance remains unclear. Other studies in paediatric surgery show a high rate of growth disturbance when damaging the growth plate. In a study analysing transphyseal drilling in skeletally immature patients with anterior cruciate ligament injury, more than 10 mm femoral length shortening of the operated leg was detected in 24% of the patients. The mean length shortening was 3.5 mm and 82% of the patients showed valgus deviation of two degrees on the operated leg [14]. Interestingly, in our study population, three of four patients who suffered a redislocation after MPFL reconstruction had trochlear dysplasia; three had an elevated TTTG distance (N15 mm) and two had patella alta with an Insall–Salvati N 1.2 and one had valgus malalignment. All of these patients showed at least two of the redislocation predicting factors. An elevated TTTG distance (N 15 mm) as well as patella alta have been identified as significant risk factors for patella redislocation after conservative treatment of first time dislocation in children [34,35]. In line with our results Steensen et al. showed that patella alta frequently co-exists with trochlear dysplasia [36]. However, Nelitz et al. performed an analysis on 37 children and adolescents with recurrent patellar instability after unsuccessful operation. Although TTTG distance and patella alta were not detected as a reason for failure, trochlear dysplasia was stated to be a major risk factor for recurrent dislocation after surgical reconstruction [37]. Due to high redislocation rates observed for MPFL reconstruction techniques with femoral soft tissue fixation, which was confirmed by our results, we see limited indication for these techniques. Only in the absence of additional risk factors such as elevated TTTG (N15 mm), patella alta, valgus or torsional malalignment, the modified adductor sling technique could be recommended as a therapeutic option for recurrent patella instability in children. Especially in cases of severe trochlea dysplasia (Déjour B–D) femoral soft tissue reconstruction techniques could not be recommended. When additional risk factors such as severe trochlear dysplasia (Déjour B–D) occur, low redislocation rates could be achieved with femoral screw fixation techniques taking into account the risk of injuring the femoral growth plate [37,33]. A limitation of the study was that no preoperative randomization was performed due to the retrospective study design. Our selection was made at the time of operation and we described the outcome postoperatively. Furthermore, follow up was only 12 months in one case. This could alter the results as recurrent dislocation can occur later than that time. Also, this study was based on a relatively small number of 30 procedures, so we cannot be certain whether this approach is superior to other surgical techniques. Another limitation is that the group of patients with failed surgery encompasses only four patients. It was not possible to perform multivariate analysis to identify interactions of different risk factors. Hence, this technique proved to be useful at short-term follow up. Also, we did not collect data regarding scores at the time before surgery; a comparison between pre- and postoperative condition of the patients could not be made. Further investigations in terms of long-term results of the modified adductor sling technique should be evaluated in future studies. 5. Conclusions The modified adductor sling technique for MPFL reconstruction in children and adolescents showed elevated redislocation rates. Only in the absence of additional patellofemoral maltracking, caused by elevated TTTG (N15 mm), patella alta or especially severe trochlear dysplasia, the modified adductor sling technique could be recommended. Acknowledgements Each author certifies that no financial support was received for this study. The study was funded by Asklepios Kliniken Hamburg GmbH (#2953). 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Please cite this article as: Alm L, et al, Modified adductor sling technique: A surgical therapy for patellar instability in skeletally immature patients, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.08.051