Medial patellofemoral ligament reconstruction for patellar maltracking following total knee arthroplasty is effective

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1 DOI /s y KNEE Medial patellofemoral ligament reconstruction for patellar maltracking following total knee arthroplasty is effective Stijn van Gennip Janneke J. P. Schimmel Gijs G. van Hellemondt Koen C. Defoort Ate B. Wymenga Received: 10 March 2012 / Accepted: 19 October 2012 Ó Springer-Verlag Berlin Heidelberg 2012 Abstract Purpose Maltracking of the patella after total knee arthroplasty (TKA) remains a well-recognized problem. The medial patellofemoral ligament (MPFL) has shown to be important for patellar stabilization and reconstructions of the MPFL have already shown excellent functional outcomes for patellar instability of the native knee. Nevertheless, there is only limited literature on using an MPFL reconstruction for correction of patellar maltracking after TKA. In this retrospective study, a consecutive case series was evaluated. Methods Between 2007 and 2010, nine patients (nine knees) with anterior knee pain and symptomatic (sub)luxations of the patella after primary or revision TKA were treated by reconstruction of the MPFL in combination with a lateral release. In two cases, an additional tibial tuberosity transfer was performed, due to insufficient per-operative correction. Pre-operative work-up included a CT scan to rule out component malrotation and disorders in limb alignment. Pre- and post-operative patellar displacement and lateral patellar tilt were measured on axial radiographs. Clinical outcome was evaluated using the visual analogue scale (VAS) satisfaction, VAS pain, dislocation rate and Bartlett patella score. Results Median patellar displacement improved from 29 mm (0 44) to 0 mm (0 9) post-operatively. Median S. van Gennip (&) G. G. van Hellemondt K. C. Defoort A. B. Wymenga Orthopaedic Surgery, St. Maartenskliniek, Postbus 9011, 6500 GM Nijmegen, The Netherlands s.vangennip@maartenskliniek.nl J. J. P. Schimmel Research Development and Education, St. Maartenskliniek, Nijmegen, The Netherlands lateral patellar tilt was 45 (23 62) pre-operative and changed to a median 15 (-3 to 21) post-operative. Median VAS satisfaction was 8 (5 9) and only one patient reported a subluxing feeling afterwards. The Bartlett patella score displayed a diverse picture. Conclusions Patellar maltracking after primary or revision TKA without malrotation can effectively be treated by MPFL reconstruction in combination with a lateral release. Only in limited cases, an additional tibial tuberosity transfer is needed. Level of evidence IV. Keywords MPFL reconstruction Patellofemoral maltracking Instability Total knee arthroplasty Realignment procedure Introduction Patellofemoral complications can occur after primary and revision total knee arthroplasty (TKA) [12]. Patellofemoral maltracking occurs when the patella does not remain in the femoral groove during motion, which results in patellofemoral pain and instability. The stability of the patellofemoral joint is affected directly by several factors, including prosthetic component position and the resultant limb alignment, preparation of the patella, prosthetic design and soft tissue balance [12]. During the 1990s, more attention was directed towards the medial patellofemoral ligament (MPFL) as one of the important medial stabilizers of the patella. Several biomechanical studies have demonstrated that the MPFL is the primary medial restraint [8, 22], and a number of clinical studies have shown that acute patellar dislocation is often associated with injuries of the MPFL [1, 9, 10, 21].

2 Buckens et al. [6] reviewed the literature and concluded that there is limited but growing evidence that a MPFLbased surgical approach to patellofemoral instability leads to excellent functional outcomes for patellar instability of the native knee. Because nonsurgical treatments (bracing, physical therapy) after primary or revision TKA are not a very effective treatment of patellofemoral maltracking, surgical intervention is the usual treatment [12]. It is important to identify the aetiology of the maltracking in order to select the appropriate surgical intervention [12]. Revision arthroplasty is justified when patellar instability can be attributed to component malrotation. In the absence of component malrotation, a lateral retinaculum release with or without vastus medialis plication or a medial repair can be executed. These procedures do not yield acceptable outcomes, whereas it is not believed to substantially improve patellar tilt or subluxation. Distal realignment has a more profound impact on alignment, but is a more invasive procedure [3 5, 14, 19]. In 2008, Asada et al. [2] first reported a case of MPFL reconstruction to treat patellar maltracking after TKA. This technique has been used in our institution since It was of interest to determine whether a realignment procedure with MPFL reconstruction would stabilize the maltracking patella in selected cases. Therefore, a consecutive case series of MPFL reconstructions for patellofemoral realignment after primary or revision TKA was evaluated. Hypothetical patellar tracking would improve according to patient satisfaction, luxation rate and measurements on axial radiographs. Materials and methods Patients Retrospectively, nine patients (nine knees) with symptomatic subluxation or dislocation of the patella and subsequent patellofemoral complaints after primary or revision TKA were identified. They had been treated in our institution between 2007 and All patients underwent a patellofemoral realignment procedure with MPFL reconstruction. Symptomatic patellar subluxation or dislocation had been the main indication for this treatment. Methods In seven patients, pre-operative work-up included a CT scan to exclude the presence of component malrotation. Both femoral and tibial component positions were measured. Tibial tuberosity trochlear groove offset (TT TG) was measured to quantify abnormal alignment of the tibial tubercle relative to the trochlear groove as an underlying cause of the instability [11, 16]. TT-TG was measured using a single image technique measuring protocol as described by Koeter et al. [17], in which an image of lines through posterior condyles and trochlear groove of the femoral component is copied to the images depicting the tibial tuberosity. In two patients, the diagnosis had been made based on clinical assessment and plain radiographs. Neither patient had an external rotation of the foot and both had stable knees in extension and flexion. Leg alignment was normal as measured during clinical assessment preoperatively. All reconstructions were combined with a lateral release: two had an additional tuberosity transfer during surgery since the soft tissue procedure alone did not completely correct the maltracking. In six patients, the MPFL reconstruction was performed using a quadriceps strip. The use of this quadriceps strip was preferred because of an easy exposure and the presence at the origin of the reconstruction site. The quadriceps tendon was identified and a strip of approximately cm in length and 1 cm width was harvested, leaving its attachment to the patella intact. In two patients a semi-tendinosus allograft and in one patient a tibialis posterior tendon allograft were used. The allografts were used if the quality of the patient s quadriceps tendon was poor. The allografts were obtained from a tissue bank and attached to the medial side of the patella using one or two anchors. A bone tunnel with soft tissue screw or anchor was used to secure the tendon end(s) that had been passed subcutaneously at the MPFL origin, between the medial epicondyle and adductor tubercle. Before graft fixation, the correct isometric position was checked through the full range of motion. If the graft was either tight in flexion or loose in flexion, the position of the graft was adjusted by moving it either distally or proximally until the correct tension was achieved. The graft was fixed at 30 of flexion leaving a mediolateral mobility of 1/3 of the patella width in order not to overconstrain the graft [23]. After surgery, the patient was mobilized with a removable cast for 6 weeks; unloaded flexion/extension exercises were performed under the supervision of a physiotherapist. To evaluate the intervention, patellar displacement (PD) and lateral patellar tilt (LPT) were measured on plain axial radiographs taken prior to and after surgery. The PD was measured (Fig. 1a, b) in relation to the femoral component [16, 18]. The LPT is the angle between the patellar width line and the reference line, which was drawn from the anterior limits of the femoral condyles (Fig. 1c, d) [15, 16]. Measurement accuracy for PD and LPT is, respectively, 1 mm and 1. The percentage agreement is, respectively, 87 and 84 % [16]. Identification of the centre of the patella was performed in the pre-operative subluxated patella

3 images. Size and shape after surgery were exactly the same as pre-operatively, because patellar shape was not altered during surgery. Patient satisfaction and (anterior) knee function were evaluated using the visual analogue score (VAS) for satisfaction and pain, luxation rate and the Bartlett patella score after the surgery [13]. Questionnaires were sent at a median interval of 33 months (10 48) to all patients. Statistical analysis Because this article concerns a consecutive case series with only nine patients, only descriptive analysis has been performed. Results The median age at the time of MPFL reconstruction was 75 years (60 83). Seven patients were women; two were men. Six of the arthroplasties in situ were primary TKAs and three were revisions. Three patients had a patellar component in situ. Radiologic evaluation was available for all nine knees at a median interval of 8 months (3 49) after realignment. For eight patients, follow-up at a median interval of 33 months (10 48) after realignment was performed using questionnaires. One patient had died of nonrelated causes during the follow-up period; she did not report any dislocations during outpatient visits at follow-up time. No joint-related complications had occurred and all wounds had healed uneventfully after surgery. Median PD improved from 29 mm (10 44) to 0 mm (0 9) post-operative. Median LPT was 45 (23 62) preoperative and changed to a median 15 (-3 to 21) postoperative. Patellar dislocations disappeared in all patients, only one patient reported twice having a feeling related to subluxation. On the VAS for satisfaction, six of the eight patients had an eight or higher; no one had a value lower than five. The VAS for pain and the Bartlett score show that while about half of the patients had relatively high scores, the others had relatively low scores. Discussion The most important finding of the present study was that a patellofemoral realignment procedure with MPFL reconstruction is an effective treatment for patellar maltracking in patients without malrotation after primary or revision TKA. Patients reported a high satisfaction about the procedure with all patients scoring higher than five and six out of eight scoring an eight or higher (median score 8). Patients improved clinically, regarding this high satisfaction, and did not experience repeated subluxations, except one patient with limited subluxation sensations. Furthermore, maltracking as measured on radiographs had decreased. Similar successful outcomes in terms of absence of anterior knee pain, functional problems and re-luxation have been described in literature, although this regards only case reports [2, 7, 20]. Exclusion of causes other than soft tissue imbalance is essential. During clinical assessment, it is important to Fig. 1 Measurement techniques: patellar displacement (PD) is the distance between the line through the centre of the femoral condyles and the line through the centre of the patella; a prior to surgery, b after surgery, lateral patellar tilt (LPT) is the angle between the patellar width line and the line from the anterior limits of the femoral condyles; c prior to surgery, d after surgery

4 exclude external rotation of the foot, which could indicate an internal rotation of the tibial component. The knee should also be stable in flexion and extension. Leg alignment should be normal. If needed, CT images can be helpful to exclude component malrotation as an underlying cause of patellar instability as had occurred for most cases in this series. An abnormal lateral position of the tibial tuberosity was diagnosed on the CT as having a TT-TG of greater than mm [11]. In such cases, we usually perform a distal realignment in combination with a lateral release and MPFL reconstruction. In the reported case series, the TT-TG was less than 15 mm as measured by CT or during surgery. In two patients, an additional tuberosity transfer was performed despite a normal TT-TG value; this was decided during surgery because the proximal realignment was not sufficient to correct the maltracking completely. Many different anatomical MPFL reconstruction techniques have been described [24, 26]. There is no consensus regarding the choice of graft, graft positioning, graft tension or static versus dynamic reconstruction [25]. In this series, a quadriceps strip or allograft with suture anchors had mainly been used, which has the advantage that a bone tunnel in the patella is not needed. If a patella button is in place, these techniques can be applied without damaging the implant. When attaching an allograft, it is important for the patellar tunnel to be eccentric in case of a patella button [7]. The insertion of the graft at the medial site of the patella and the origin between the medial epicondyle and adductor tubercle is chosen because this is the natural position of the ligament. Fixing the graft at 30 degrees of flexion is important because in this position the stabilizing role of MPFL is the most prominent in patellar stability [23]. Rehabilitation using a removable cast and flexion/ extension exercises for 6 weeks is chosen, because the graft needs time to secure at the insertion sites and stiffness of the knee is prevented by the exercises. Limited data are available in the literature concerning the failure of an MPFL reconstruction. Known complications are patellar fractures and graft failure accompanied by recurrent patellar dislocation [27]. In this series, complication rate was low with only one patient with two subluxation episodes; there were no fractures or wound problems. Many methods are available to evaluate lateralization and/or tilt on axial radiographs. The PD and the LPT were used since they have proven reproducibility and are clinically relevant [16]. All radiographs in this study had a sufficient interval (a minimum of 3 months) between the intervention and the moment of radiological control. Hence, post-operative swelling would not have influenced our results. In the absence of component malrotation or bony malalignment, the cause of patellar instability is unclear in most cases. We think that a possible cause is stretching or rupture of medial structures that are closed after implantation of the TKA. Alternatively, some resorbable sutures may have lost strength too quickly or in some patients the medial retinaculum might rupture or stretch due to the high pressure from a large haematoma. In other patients, we have seen rupture after forcefully flexing the knee during a fall. Currently, we use 3 4 nonresorbable sutures in the MPFL area at the proximal 1/3 of the patella when we close a medial arthrotomy. Conclusion Patellar maltracking after TKA without component malrotation can be effectively treated with a lateral release and an anatomic medial patellofemoral ligament reconstruction. Only in limited cases, an additional tibial tuberosity transfer will be necessary. References 1. 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