Stepwise lengthening of quadriceps extensor mechanism for severe obligatory and ﬁ xed patella dislocators: Four-year clinical and surgical outcomes

Objectives: The purpose of this study was to report clinical and surgical outcomes of medial patellofemoral ligament reconstruction (MPFLR) and concomitant quadriceps lengthening to treat ﬁ xed and obligatory patellofe-moral instability (PFI) in the pediatric population. Methods: Patients with obligatory or ﬁ xed PFI who underwent simultaneous MPFLR and quadriceps lengthening from 2008 to 2020 were reviewed. Of the 413 records, 24 ﬁ t the inclusion criteria. Demographic information, surgical details, associated diagnoses, and outcome measures were collected for each knee. Complications and additional surgeries were also obtained. Results: The ﬁ nal cohort included 20 patients (10 male, 10 female), with a total of 24 knees. The average age at the time of surgery was 11.9 (cid:1) 3.1 (5.4 – 17.3). Seventeen were obligatory dislocators in ﬂ exion and 7 were ﬁ xed dislocators. Average follow-up was 4.3 (cid:1) 2.4 (1.3 – 9.4) years. One patient was lost to follow-up and excluded from the study. The mean outcome measures were as followed; KOOS 82, HSS Pedi-FABS 9, IKDC 76, Kujala 78, BPII 67, and SANE 90. Six patients had subsequent instability episodes. Ten patients had a subsequent surgery. Conclusions: Reports on quadriceps lengthening to treat PFI in the pediatric population are rare. Six (25 %) of the 24 knees included had subsequent PFI. Although this is a high rate of recurrent instability, no second surgeries were indicated for infection, extensor mechanism weakness, or contracture. The authors conclude that simultaneous MPFLR and stepwise quadriceps lengthening can be used to effectively manage ﬁ xed and obligatory PFI in this dif ﬁ cult patient population. Level of evidence: IV.


Introduction
Fixed and obligatory lateral patellar dislocators present with pathologic morphological anatomic risk factors, tight lateral structures, and often with a shortened extensor mechanism that contribute to patellofemoral instability (PFI) [1,2].Fixed dislocations refer to an irreducible lateral dislocation throughout knee range of motion.Obligatory dislocation in flexion refers to patients whose patella dislocates laterally every time their knee flexes.If left untreated, both types of PFI may lead to degenerative arthritis [3].Nomenclature of these rare types of PFI can be confusing, as historically, these patients have been referred to as congenital, habitual, or syndromic dislocators [4].It is our preference to use the terms fixed patellar dislocation and obligatory dislocator in flexion.
Different techniques have been published to guide treatment.However, due to the severe nature of both fixed and obligatory PFI, medial patella femoral ligament (MPFL) reconstruction alone is not enough to neutralize the deforming forces on the patella, resulting in the need for concomitant procedures, such as extensive lateral release and quadriceps tendon lengthening.Clinical reports of quadriceps lengthening techniques in the setting of pediatric PFI are few.In 1976 Stanisavljevic et al. described one of the first techniques consisting of a proximal extensive sub-periosteal realignment of the quadriceps mechanism, medial plication, and an additional distal Roux-Goldthwait patellar tendon realignment procedure [5].At 2-year follow-up, they reported satisfactory results in 6 knees.However, few small cohort studies have been able to replicate this technique with good outcomes, and the largest cohort to date reported recurrence of instability in 80 % [6][7][8][9][10][11].
Our approach, previously described by Andrish in 2007 and Ellsworth et al., in 2021, begins with an extensive lateral release followed by a stepwise lengthening of the extensor mechanism.If, after lateral retinacular lengthening and vastus lateralis tendon lengthening, the patella continues to dislocate laterally with knee flexion, then a formal quadriceps Z-lengthening is performed to address the shortened extensor mechanism and neutralize the lateral vector of force on the patella during knee flexion [1,12].An MPFL reconstruction is then performed.
This study aimed to explore the effect of concomitant MPFL reconstruction, lateral retinacular release and quadriceps lengthening and review the surgical outcomes of pediatric patients following this procedure.We hypothesize that simultaneous MPFL reconstruction, lateral retinacular release, and quadriceps lengthening will be an effective and safe procedure to treat fixed and obligatory PFI in the pediatric population.

Study cohort
After institutional review board approval, all operative records of MPFL reconstructions performed by the senior author (D.W.G.) from 2008 to 2020 were retrieved using CPT codes.Patients who presented with obligatory or fixed patellar instability and underwent simultaneous MPFL and quadriceps lengthening with minimum two-year follow-up were reviewed.Eligible patients were contacted and asked to participate in the study.Demographic information, surgical details, associated diagnosis, and outcome measures were collected for each knee.

Surgical technique
The surgical technique used for this series of patients with obligatory or fixed PFI included a standard MPFL reconstruction in addition to an extensive lateral release, vastus lateralis lengthening (Fig. 1), and a separate Z-lengthening of the rectus and intermedius tendon (Fig. 2) which has previously been published and is briefly described here [1].
Briefly, a double-limbed MPFL reconstruction was performed using either hamstring allograft or autograft.The senior author's preferred technique involves harvesting and preparation of the graft followed by reaming two short sockets in the superior half of the patella.A guidewire is then used to determine the location of the epiphyseal femoral socket.The location is confirmed using palpation, isometrics, and fluoroscopy as described by Ladenhauf and Schottle prior to reaming the socket [13,14].The single limb of the graft is then secured in the femoral socket using a nonabsorbable tenodesis screw.The double-ended limb of the graft is then passed between layers 2 and 3 of the knee, and each of the limbs is secured into the patella using tenodesis screws.Alternatively, the superior limb of the graft can be sutured to the quadriceps tendon.
Distal realignment procedures included the Galeazzi procedure, tibial tubercle osteotomy, medial patella tibia ligament reconstruction (MPTL), and the Garin procedure.Briefly, the Galeazzi procedure was performed by harvesting the semitendinosus tendon proximally while leaving the tendon attached to the pes anserinus distally.The tendon was then brought through a 4.5 mm longitudinal tunnel in the medial patella from distal to proximal and the remainder of the limb was secured to the medial epicondyle of the femur with either a suture anchor or suture into the adductor tendon.Tibial tubercle osteotomy was performed by first identifying the medial and lateral borders of the patellar tendon.A subperiosteal dissection was carried out laterally on the proximal tibia.The tibial tubercle was isolated, and with a combination of osteotomes and a saw, a 6 cm wedge of the tibial tubercle was then cut and translated medially and secured with 3.5 mm screws.The MPTL procedure was performed using the residual semitendinosus tendon allograft from the MPFL reconstruction.This was secured 2 cm medial to the tibial tubercle into the proximal tibial epiphysis with a suture anchor placed under fluoroscopy and again supplemented with numerous non-absorbable sutures.The graft was then brought to the inferomedial border of the patella and secured with multiple sutures.The Garin procedure was performed by detaching the patellar tendon from the tibial tubercle with care to avoid the apophysis and securing it medially with a suture to the periosteum and a supplemental suture anchor.

Post-operative management
Following surgery, patients were placed in a hinged brace locked in extension for 4-6 weeks while allowed to partial weight bear as tolerated with crutches for support.At week 2, they were allowed to begin physical therapy with the goal of achieving 90 degrees of flexion by week 4.After six weeks, patients were allowed to walk without a brace.Functional progression to running and jumping was typically started after four months post-operatively.

Outcome measures
At a minimum 2-year follow-up, PRO measures included Knee Outcome in Osteoarthritis Survey (KOOS/KOOS-Child), HSS Functional Activity Brief Scale (HSS Pedi-Fabs), International Knee Documentation Committee (IKDC/Pedi-IKDC), Kujala Anterior Knee Pain Scale (Kujala), Banff Patellofemoral Instability Instrument (BPII) and the Single Assessment Numeric Evaluation (SANE).Except for the HSS Pedi-Fabs, which was scored 0 to 30 (30 meaning fully active), all other outcomes measures were scored 0 to 100 (100 meaning no symptoms or disability).Follow-up complications and additional surgeries were also obtained.

Statistical analysis
Statistical analyses were performed using the Statistical Package for Social Sciences (SPSS) version 22.0 (IBM Corp., Armonk, NY).Continuous variables were reported as means and standard deviations, and discrete variables were reported as frequencies and percentages.

Results
Of the 413 operative records analyzed, 24 knees underwent simultaneous MPFL and quadriceps lengthening.The final cohort included 20 patients (10 male, 10 female).The average age was 11.9 AE 3.1 (5.4-17.3).Fourteen right knees and 10 left knees were included.Seventeen were obligatory dislocators, and 7 were fixed dislocators.Average follow-up was 4.3 AE 2.4 (1.3-9.4) years (Table 1).One patient was lost to follow-up and excluded from the study.
Surgical technique differed slightly among this cohort.Four (17 %) were revision cases that had had prior MPFL surgery.Of the 24 knees evaluated, 14 (58 %) underwent Z-lengthening of the main quadriceps tendon (rectus femoris and vastus intermedius tendons).All knees (100 %) underwent vastus lateralis tendon lengthening.In addition to quadricepsplasty, all knees had lateral retinacular release, with 9 (38 %) knees having a repair of the lateral retinaculum in a lengthened position, ie a lateral retinacular lengthening.
Seven knees (29 %) underwent concomitant distal realignment procedures of which 2 (17 %) were Galeazzi procedures, 2 (4 %) were tibial tubercule osteotomies (TTO), 1 (4 %) had a medial patella tibia ligament reconstruction (MPTL), 1 (4 %) had a transfer of patella tendon from the tibial tubercle to a more medial portion of the epiphysis and an MPTL reconstruction, and 1 (4 %) had a Garin procedure.Three (13 %) patients had hemi-epiphysiodeses, 3 (13 %) had partial meniscectomies, 1 (4 %) had an osteochondroma excision, and 2 (8 %) had removal of hardware (ROH).The indications for a distal realignment procedure were a Fig. 2. If a Z-lengthening is indicated, a Z cut of the quadriceps tendon is performed.The distal aspect of the Z is at the superolateral aspect of the patella and spans half the transverse width of the quadriceps tendon, leaving the medial quadriceps tendon attached to the superomedial patella (A).The longitudinal aspect of the Z is in the center of the tendon, and the proximal aspect of the Z is medial.The tendon is typically lengthened about 2 cm (B).The quadriceps tendon is then repaired, and the distal aspect of the vastus lateralis is then re-attached to the lateral aspect of the main quadriceps tendon, proximal to the patella (C).Fig. 1.Operative images of the vastus lateralis lengthening procedure.The vastus lateralis tendon is identified, and the distal aspect is released from the superolateral patella (A), the adjacent quadriceps tendon, the lateral synovial bands, and the lateral intermuscular septum so that it can be completely mobilized proximally (B).laterally deviated tibial tubercle or severe patella alta.The indications for hemi-epiphysiodesis were pathologic genu valgum in patients with greater than 2 years of predicted growth remaining.
Six patients (6 knees, 25 %) had subsequent instability episodes, of which only 2 returned to having obligatory patellar instability, and 9 patients (10 knees, 42 %) had a subsequent surgery.Of note, the PROs of these patients were included in our results.Five (21 %) were revision MPFL procedures, 1 (4 %) underwent hemi-epiphysiodesis and subsequent ROH, 2 (8 %) were ROH for previous hemi-epiphysiodesis procedures, 1 (4 %) was ROH for TTO, and 1 (4 %) was chondroplasty.One patient who presented with obligatory instability and ligamentous laxity was treated non-operatively following instability episodes as they are clinically doing well.
Of the patients that underwent a revision MPFL procedure, 1 had a concomitant TTO procedure, 1 had ROH for a previous hemiepiphysiodesis and 1 underwent surgery at a different institution.One patient who underwent revision MPFL had a preoperative flexion contracture of 7 that did not improve after surgery.No other patients in this cohort reported flexion contracture or quadriceps weakness following quadricepsplasty.A summary of the surgical information can be found here (Table 2).A break-down of the procedures each patient underwent can be found here (Appendix 1).Of note, 2 of the 5 patients that underwent revision MPFL had an associated syndromic diagnosis.
Of the 20 patients included in this study, 5 had communication deficits and were unable to complete the PROs.Of the remaining 15, 12 completed PROs (80 %).Three did not return complete surveys.The mean outcome measures were as followed (Table 3); KOOS 82, HSS Pedi-FABS 9, IKDC 76, Kujala 78, BPII 67, and SANE 90.

Discussion
The purpose of this study was to review surgical outcomes of skeletally immature patients with fixed or obligatory PFI that had undergone a stepwise lengthening of the extensor mechanism and highlight the efficacy and safety of this procedure.
Due to the low prevalence of these conditions, there is no standard treatment algorithm in the literature.Moreover, fixed, and obligatory PFI are often associated with syndromic conditions such as Nail-Patella syndrome, Down syndrome, and Rubinstein-Taybi, which make them particularly challenging to manage.In order to neutralize these deforming forces of the short quadriceps extensor mechanism concomitant procedures are often required such as quadriceps lengthening.
Described quadriceps lengthening techniques for pediatric patellar instability are few, however, recent studies have demonstrated encouraging results.In a study including 12 patients (15 knees), Sever et al. performed a modified Stanisavljevic technique that included a Roux-Goldthwait distal realignment, subperiosteal quadriceps realignment and soft tissue medial plication [15].One patient (8 %) presented with recurrent patellar instability which occurred following a fall in the early postoperative stage.At 46.2 months follow-up, post-operative knee extension and quality of life (measured by the Pediatric Outcome Data Collection Instrument) had significantly improved.
Utilizing a separate novel technique, Danino et al. performed a "fourin-one" procedure on 34 patients (46 knees) which included a combination of Roux-Goldthwait procedure, vastus medialis obliquus (VMO) advancement, lateral release, and Galeazzi procedure [2].Six patients presented with recurrent instability (18 %).Sixteen patients (22 knees) responded to a phone interview and follow-up questionnaire, of which 91 % returned to sports at an average of 23.1 weeks follow-up.After utilizing the "four-in-one" technique on 6 knees, Joo et al. observed no recurrence of instability at 54.5 months follow [16].
Both Sever et al. and Danino et al. reported a low incidence of patellar instability recurrence and neither reported extensor lag following surgery.Additionally, in a recent 2022 study Hire & Parihk described another "four-in-one" procedure consisting of quadricepsplasty are lateral retinacular releases and lengthening, Roux-Goldthwait patellar tendon hemi-transfer, modified Insall's proximal "tube" realignment, and quadriceps slide-lengthening [11].Notably, all 3 techniques outlined in these studies deferred from performing an MPFL reconstruction, and instead used VMO advancement with concomitant realignment procedures, demonstrating that there may be multiple effective techniques to treat these complex cases.
To our knowledge, this is the first study describing surgical outcomes and complications after MPFL reconstruction and concomitant quadriceps lengthening in skeletally immature patients.We prefer the Table 2 Surgical information of the included cohort.
technique outlined in this study as we believe that by utilizing a stepwise approach, one can tailor the degree of quadriceps lengthening to the patient's level of contracture.Moreover, the diversity of underlying etiologies and associated diagnoses within this series further demonstrates that this technique is a comprehensive method of managing fixed and obligatory dislocators.
Although our rate of subsequent instability was 25 %, recent studies performing similar surgical treatment have shown a range of recurrent instability of 0-33 % (Table 4).
Additionally, none of the patients in this cohort experienced permanent extensor mechanism lag or flexion contracture.Our patients reported good objective and subjective outcomes, which demonstrate that the technique utilized is an effective approach to treat fixed and obligatory PFI.Despite including subsequent cases of instability, the PROs reflect good subjective outcomes at mean 4-year follow-up.We speculate that our relatively high instability rate seen in this cohort may be due to the high percentage of syndromic and non-verbal patients (45 % and 25 %, respectively).We also speculate that more aggressive use of distal realignment procedures when anatomically indicated (ie.were a laterally deviated tibial tubercle or severe patella alta) and the addition of an MPTL reconstruction to the MPFL reconstruction may reduce the postoperative instability rate going forward.This study has limitations that must be acknowledged.Due to the retrospective nature of the methods, information regarding all patients could not be captured.Five patients were unable to complete them due to communication deficits, of the remaining 15, only 80 % completed the PROs.Three patients did not return complete surveys.Moreover, preoperative PROs were not collected, preventing any evaluation of improvement in individual scores.Secondly, the small cohort of subjects obtained from a single institution and surgeon prevents us from generalizing the results obtained, and the numerous secondary procedures the patients underwent prevented us from performing a power analysis or obtaining strong statistical conclusions.Finally, the minimum follow-up was relatively short, that is 16 months, though most of our patients had over 2 years of follow-up (75 %).

Conclusion
Reports on quadriceps lengthening to treat patellar instability in the pediatric population are rare.Six (25 %) of the 24 knees presented in this retrospective cohort had subsequent instability.Only 2 (8 %) returned to having obligatory patellar instability.Although this is a high rate of recurrent instability, no second surgeries were indicated for infection, extensor mechanism weakness, or contracture.Moreover, despite the relatively high second surgery rate, the clinical and PROs were good.The authors conclude that MPFL reconstruction and simultaneous quadriceps lengthening can be used to effectively manage fixed and obligatory patellar dislocation.To our knowledge, this is the first reported cohort to provide these outcomes for skeletally immature patients.

Declaration of competing interest
The authors declare the following financial interests/personal relationships that may be considered as potential competing interests.
Daniel W. Green reports a relationship with Arthrex Inc that includes: consulting or advisory and equity or stocks.Daniel W. Green reports a relationship with Pega Medical that includes: equity or stocks.