Abstract
Surgical treatment of patellar dislocation poses a challenge in skeletally immature patients. The traditional approach of lateral release and medial imbrication carries a high probability of recurrence. Medial patellofemoral ligament reconstruction recently has become a popular procedure for patellofemoral instability, but its broad application in immature skeletal systems is limited by the risk of injury to epiphyseal plate. Herein, we describe an alternative surgical strategy whereby medial patellar retinaculum cable transfer is done in conjunction with anchoring suture reinforcement and medial tightening. We first harvest the longitudinal retinaculum cable situated along medial patella, dissecting the distal end and leaving the proximal attachment to quadriceps tendon insertion intact. The free end of medial patellar retinaculum cable is then transferred to medial femoral condyle (distal to growth plate) through a soft-tissue tunnel (superficial to capsule) and fixed by absorbable suture anchor. The latter allows suture reinforcement of medial patella via bone tunnels. Finally, the vastus medialis oblique muscle and remaining medial patellar retinaculum are fastened through bone tunnels onto patella. This technique is simple and reproducible, avoiding the risk of growth plate injury.
Technique Video
The incidence of patellar dislocation (PD) is roughly 42 per 100,000 population, with skeletally immature children and adolescents more often affected.1 Nonoperative treatment is associated with a high rate of recurrence (30%-70%) that peaks in younger individuals.2 Despite a growing trend among such patients toward surgical treatment of PD,3, 4, 5 procedures most commonly applied to adults, such as medial patellofemoral ligament (MPFL) reconstruction, demand caution because of the substantial risk of growth-plate damage,6 especially in the hands of inexperienced surgeons. Lateral release and medial imbrication are thus generally preferred, although the potential for relapse is high.
We have subsequently devised a strategy for treating skeletally immature patients with PD. Medial patellar retinaculum cable (MPRC) transfer is performed, in conjunction with anchoring suture reinforcement, vastus medialis oblique (VMO) muscle advancement, and medial patellar retinaculum (MPR) tightening (Fig 1). Our technique uses the redundant MPR to compensate for traction exerted on medial aspect. A distally deployed suture anchor serves to safeguard the distal femoral epiphyseal plate and limit range of motion. This is a safe and reproducible approach for treating skeletally immature patients that does not require fluoroscopy. The study was approved by the Ethics Committee of the First Affiliated Hospital of the University of South China.
Fig 1.
Schematic of surgical PD correction performed on left knee. (A) MPRC landmark and (B) postoperative view. (MPRC, medial patellar retinaculum cable; PD, patellar dislocation; PT, patellar tendon; QT, quadriceps tendon; VMO, vastus medialis oblique.)
Surgical Technique
Patient Positioning
Patients are positioned supine on the operating table and administered spinal or general anesthesia. A tourniquet inflated to 50 to 55 kPa is placed on the proximal thigh.
Surgical Approach
Diagnostic arthroscopy initially is undertaken to debride hematoma and check for intra-articular patellofemoral osteochondral injuries, removing small osteochondral fragments. Larger fragments (>10 mm across) may be later openly reduced and fixed by way of a subsequent medial patellar incision. Patellar tracking is also evaluated through full range of motion.
The first skin incision (4-5 cm) is made along medial patella (Fig 2). MPR is then separated at the medial patellar rim, from superior patellar edge distally to a point 1 cm beyond. Any large osteochondral fragments (as mentioned previously) requiring reduction/fixation are addressed through this incision. Another incision is made running parallel and 1 cm medially to medial edge of patella, extending from 1 cm distal to patella to VMO insertion in proximity (VMO tendon insertion remaining in part). Next, the soft-tissue cable is dissected distally, and a segment of longitudinal MRPC is harvested (approximate size: length, 5 cm; width, 1 cm) while leaving its proximal attachment to quadriceps tendon insertion intact. The free distal end of MPRC is afterwards whipstitched (Fig 3).
Fig 2.
Right knee, supine position, lateral view on medial side. Landmarks of skin incisions are shown, one along medial patella (4-5 cm) and another (2 cm) overlying medial femoral epicondyle.
Fig 3.
Right knee, supine position, lateral view on medial side. Harvested medial patellar retinaculum cable (approximate size: length, 5 cm; width, 1 cm) is shown, leaving proximal attachment to quadriceps tendon insertion intact and whipstitching distal end.
Implanting the bioabsorbable suture anchor (HEALIX, 4.5 mm; Depuy Mitek, Raynham, MA) in the medial femoral condyle calls for an overlying incision (2 cm) (Fig 2), installing the anchor just distal and posterior to medial epicondyle (Fig 4). The distal end of MPRC is thereafter pulled via second incision through a soft-tissue tunnel between articular capsule and MPR (Fig 5). It is lasso sutured by anchoring sutures and secured to medial collateral ligament using a VICRYL suture (Ethicon, Somerville, NJ) (Fig 6).
Fig 4.
Right knee, supine position, lateral view on medial side. Bioabsorbable anchor suture (4.5 mm) is inserted into the medial femoral condyle, distal to epicondyle.
Fig 5.
Right knee, supine position, lateral view on the medial side, is shown. Whipstitched medial patellar retinaculum (MPR) cable is pulled via a second skin incision through the soft-tissue tunnel between the articular capsule and MPR.
Fig 6.
Right knee, supine position, lateral view on medial side. Medial patellar retinaculum cable is lassoed by anchoring sutures and reinforced to medial collateral ligament (VICRYL suture).
To complete the procedure, 2 bone tunnels must be created at upper- and middle-third of medial patellar border. The other set of anchoring sutures is pulled to medial edge of patella through the soft-tissue tunnel, introduced into the bone tunnels, and tied at ∼30° to 60° of knee flexion (Fig 7) so that the patella is maintained within center of femoral trochlear groove. The remaining VMO tendon insertion is pulled distally and sutured to the bone tunnels using #2 ETHIBOND (W4843, 75 mm; Ethicon) (Fig 8), similarly tightening the rest of MPR to medial edge of patella (Fig 9). Finally, patellar position and soft-tissue tension are checked at full flexion and extension, performing lateral release (if tightening is palpable); and the patient’s patellar tracking is arthroscopically confirmed (Table 1).
Fig 7.
Right knee, supine position, lateral view on medial side. Anchoring sutures are pulled to the medial edge of patella (through the soft-tissue tunnel), then introduced into bone tunnels and tied at ∼30° to 60° of knee flexion.
Fig 8.
Right knee, supine position, lateral view on medial side. Distal end of vastus medialis oblique muscle is pulled distally and sutured to bone tunnels on the patella.
Fig 9.
Right knee, supine position, lateral view on medial side. Suturing of remaining medial patellar retinaculum to medial edge of patella through bone tunnels is shown.
Table 1.
Procedural Pearls and Pitfalls
| Pearls | Pitfalls |
|---|---|
| Sufficient strength of the medial patellar retinaculum cable (MPRC) | Suture anchor implanted too high to avoid growth plate injury |
| Implantation of suture anchor just distal and posterior to femoral epicondyle | Overtensioning of MPRC and anchoring sutures |
| Anchoring sutures introduced into bone tunnels and tied at ∼30° to 60° of knee flexion, with suitable tension | |
| Vastus medialis oblique insertion pulled distally and sutured to bone tunnels of patella |
Postoperative Protocol
Treated limbs are immobilized for 4 weeks using an adjustable knee brace. Straight-leg elevation, ankle pump, and heel translation are all initiated as soon as possible after surgery, along with partial weight-bearing (crutch protected). Passive knee flexion of 30° during the first 2 weeks is increased by 30° per week to reach 90° after 4 weeks. Full weight-bearing and walking begin 4 weeks postoperatively, allowing a return to daily life by postoperative month 3. Resumption of sports is restricted to 6 months at minimum.
Discussion
Surgical methods of choice for PD may be problematic for skeletally immature patients. The probability of recurrent patellar instability is high after traditional lateral release and medial imbrication procedures. Operative repair of an MPFL injury significantly reduces the redislocation rate but does not improve subjective or objective knee function compared with a knee brace alone.2 Although some sources have reported safe and effective outcomes for MPFL reconstructions in skeletally immature patients with PD, femoral fixation of implants may be challenging because of the nearness of MPFL insertions and growth plates7; and chances of redislocation or subsequent knee injury are greater in immature (vs adult) patients.3,8
Recently, the importance of the medial quadriceps tendon femoral ligament in restoring patellar stability has been underscored.9,10 In our approach, the MPRC is connected to quadriceps tendon proximally, affixing the distal end to medial femoral condyle. The MPRC acts to pull the quadriceps medially, functioning quite similar to medial quadriceps tendon femoral ligament reconstruction. MPFL reconstruction using pedicled quadriceps tendon autograft yields similar clinical and patient-reported outcomes compared with gracilis tendon11,12; our MPRC transfer technique is similar with pedicled quadriceps tendon autograft MPFL reconstruction.
Our implanted suture anchor resides distal to medial femoral epicondyle, away from the original MPFL insertion and just beyond the growth plate, eliminating the need for fluoroscopy. The anchoring sutures also are secured to medial patella, tending to tighten the implant in knee extension only and imparting a low risk of restriction in flexion. We tend to agree with the “favorable anisometry” concept, given the implant’s looseness during flexion (patella fully engaged in trochlear groove), while tightened in extension.5 Its slight distal positioning tends to pull the patella distally and medially and is particularly effective for patella alta, a major PD risk factor in children. In addition, its absorbability helps reduce the risk of growth plate interference and prevent excessive medial stretching as the knee develops.
The VMO is a critical branch of the quadriceps muscle, a structure is primarily responsible for normal patellar trajectory dynamics. Senavongse and Amis13 have found that relaxation of the VMO lowers resistance to patellar excursion by 30%, offering a 20° to 90° range of knee flexion. In patients with patellar instability, the distal end of VMO is set higher than in healthy counterparts.14 Hence, we simultaneously shifted the VMO insertion downward and sutured it to patella, serving to increase VMO-exerted patellar traction.
The pathology of PD is largely ascribed to elongation and loosening of the MPR. Traditional MPFL repair or medial imbrication procedures involve overlap of the redundant medial retinaculum, creating a glut of soft tissue at medial patella. In our procedure, the redundant MPR is severed and transferred to medial femoral condyle. Once the gap between edge of patella and remaining MPR is closed, and medial tightening is achieved, there is an observable cosmetic effect.
In summary, we have devised a treatment alternative for skeletally immature patients with PD in which MPRC is transferred to medial femoral condyle. Anchoring suture reinforcement, VMO advancement, and medial tightening are also involved. This approach is simple, safe, and minimally invasive, avoiding the risk of distal femoral growth-plate injury and eliminating the need for fluoroscopy (Table 2). However, the long-term efficacy entailed must be further examined.
Table 2.
Procedural Advantages and Disadvantages
| Advantages | Disadvantages |
|---|---|
| Simple and safe, avoiding risk of injury to distal femoral growth plate and eliminating need of fluoroscopy | Risk of injury to medial collateral ligament |
| Use of redundant retinaculum to bolster medial patellar traction, without additional implant | Inability to correct bone deformity in patellar dislocation |
| Downward shift of vastus medialis oblique (VMO) insertion, increasing VMO-exerted patellar traction | |
| Low risk of patellar fracture because of small-caliber bone tunnels |
Disclosures
All authors (Z.D., Z.Y., Z.G., D.C.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding
Project funds supplied by the Project of Health Commission of Hunan Province (No: 20201907).
Acknowledgments
The authors thank Dr. Weijie Fan for preparation of the manuscript. Data and materials of the datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Footnotes
Z.D., Z.Y., and Z.G., are co-first authors.
Supplementary Data
Patellar tracking is first evaluated under arthroscopy. The first skin incision (4-5 cm) is made along medial patella. The medial patellar retinaculum (MPR) is then separated at medial patellar rim, from superior patellar edge distally to a point 1 cm beyond. Another incision is made running parallel and 1 cm medially to medial edge of patella, extending from 1 cm distal to patella to vastus medialis oblique (VMO) insertion in proximity. Next, the soft-tissue cable is dissected distally, its proximal attachment to quadriceps tendon insertion intact. The free distal end of MPRC is afterwards whipstitched. Then, another 2-cm skin incision overlying the medial femoral epicondyle is performed. The bioabsorbable suture anchor is implanted just distal and posterior to medial epicondyle. The distal end of the MPRC is thereafter pulled via second skin incision through a soft-tissue tunnel between the articular capsule and MPR. It is lassoed by anchoring sutures and secured to medial collateral ligament using a VICRYL suture. The other set of anchoring sutures is pulled to medial edge of patella through the soft tissue tunnel. Two bone tunnels must be created at upper- and middle-third of medial patellar border. The sutures are introduced into the bone tunnels and tied at ∼30° to 60° of knee flexion. The remaining VMO tendon insertion is pulled distally and sutured to the bone tunnels using a no. 2 ETHIBOND, similarly tightening the rest of MPR to medial edge of patella. Finally, patellar position and soft-tissue tension are checked at full flexion and extension. Patellar tracking is then evaluated under arthroscopy (Right knee, supine position, lateral view on medial side).
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Patellar tracking is first evaluated under arthroscopy. The first skin incision (4-5 cm) is made along medial patella. The medial patellar retinaculum (MPR) is then separated at medial patellar rim, from superior patellar edge distally to a point 1 cm beyond. Another incision is made running parallel and 1 cm medially to medial edge of patella, extending from 1 cm distal to patella to vastus medialis oblique (VMO) insertion in proximity. Next, the soft-tissue cable is dissected distally, its proximal attachment to quadriceps tendon insertion intact. The free distal end of MPRC is afterwards whipstitched. Then, another 2-cm skin incision overlying the medial femoral epicondyle is performed. The bioabsorbable suture anchor is implanted just distal and posterior to medial epicondyle. The distal end of the MPRC is thereafter pulled via second skin incision through a soft-tissue tunnel between the articular capsule and MPR. It is lassoed by anchoring sutures and secured to medial collateral ligament using a VICRYL suture. The other set of anchoring sutures is pulled to medial edge of patella through the soft tissue tunnel. Two bone tunnels must be created at upper- and middle-third of medial patellar border. The sutures are introduced into the bone tunnels and tied at ∼30° to 60° of knee flexion. The remaining VMO tendon insertion is pulled distally and sutured to the bone tunnels using a no. 2 ETHIBOND, similarly tightening the rest of MPR to medial edge of patella. Finally, patellar position and soft-tissue tension are checked at full flexion and extension. Patellar tracking is then evaluated under arthroscopy (Right knee, supine position, lateral view on medial side).