1 Introduction

Patellar instability is an uncommon but disabling knee pathology with an incidence ranging from 6 per 100,000 in the adult population to 43 per 100,000 in the pediatric population [C2]. It can be classified predominantly into four groups: Acute traumatic dislocation, habitual/obligatory dislocation, recurrent dislocation, and congenital fixed dislocation. Acute traumatic dislocation can also result in recurrent/habitual instability of the patella in 38.4 % of the pediatric and adolescent population.² The etiology of habitual and recurrent patellar instability can be traumatic or atraumatic. Atraumatic factors consist of Genu valgum or recurvatum, external Tibial torsion deformity, Trochlear/lateral condylar dysplasia or hypoplasia, increased Femoral anteversion, generalized ligamentous laxity, and syndromes like Down's Syndrome, Turner's Syndrome, and William's Syndrome.^3–6 Most of these patients are initially asymptomatic and usually present when they begin walking. Anatomical and pathological variations commonly encountered in chronic cases of patellar instability consist of lateral patellar retinacular tightness, subdermal fascial bands on the lateral aspect of the thigh, fibrosed vastus lateralis, and deficient Vastus Medialis Obliquus (VMO) or Medial Patello-Femoral Ligament (MPFL).

Since the days of Williams (1968), multiple surgical techniques have been utilized for patellar realignment, among which are Proximal tube realignment by Insall et al.,⁷ the Roux-Goldthwait procedure,⁸ MPFL reconstruction,^9–11 and Galeazzi's semitendinosus (ST) tenodesis. Initial results following these procedures in isolation were unsatisfactory due to high recurrence rates.¹² To overcome these shortcomings and given the elusive, multifactorial etiology, Joo et al.¹³ advocated the 4-in-1 procedure for the first time in 2007. The initial 4-in-1 procedure consisted of lateral retinacular release, proximal tube realignment, semitendinosus tenodesis (STT), and Roux Goldthwait with partial patellar tendon transfer. Subsequently, multiple modifications were made to the initial description, noteworthy of which are the distal advancement of the VMO instead of proximal tube realignment and Yercan's method for reconstruction of the MPFL in skeletally immature patients.¹⁴

In this study, we utilized this modified 4-in-1 procedure, including Roux Goldthwait's procedure, lateral retinacular release, VMO advancement, and Yercan's MPFL reconstruction, and studied its functional results.

2 Materials and Methods

A total of 7 cases of pediatric atraumatic habitual patellar dislocation were included in this study, after obtaining informed written consent from the parents/guardians of the patients. Inclusion criteria: Skeletally immature patient with open physis, no history of previous surgery around the knee, and absence of fixed dislocation of the patella. All the patients underwent a formal Orthopaedic examination by two authors separately. Imaging in the form of AP, lateral, and skyline views of plain radiographs (Fig. 1), along with MRI for assessment of the MPFL, was performed. Kujala scoring was used pre- and post-operatively to assess the knee functionality. Throughout the study, we adhered to the principles of good clinical care and the guidelines of the Helsinki Declaration.

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Fig. 1 Radiographic Assessment: (a) Pre-operative Orthoroentgenogram (pelvis to ankle); (b) Pre-operative Xray Knee-AP and Lat views; (c) Pre-operative Xray Skyline view showing dislocated patella and Sulcus Angle of 150°.

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2.1

2.1 Surgical procedure

All patients underwent a 3–6 month preoperative physiotherapy regimen for symptomatic relief and quadriceps strengthening. All surgeries were performed by the paediatric orthopaedic surgeon (Figs. 2 and 3) under spinal anaesthesia in the supine position and with a tourniquet. A midline vertical skin incision from the junction of the middle and distal 1/3rd of the thigh to the patellar insertion on the tibial tuberosity was taken. Medial and lateral subcutaneous flaps were raised, dividing the subdermal fascial bands on the lateral aspect. The musculotendinous junction of the thinned-out vastus medialis was identified and separated from the quadriceps tendon. This muscular flap will be advanced distally subsequently. After the release of subdermal fascial bands, one to two transverse incisions were made over the distal 1/3rd of the vastus lateralis tendon to decrease the lateral pull. Utmost care should be taken to avoid compromising the integrity of the tendon.

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Fig. 2 Intra-operative Images showing Modified 4-in-1 technique: (a) Raised Medial and lateral flaps; (b) Lateral release; (c) Identification of Adductor Magnus Tendon; (d) Split Patellar Tendon; (e) Free ST graft passed transversely through patella; (f) Fixation of Graft.

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Fig. 3 Schematic diagram representing the steps of the surgery.

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As described in Roux Goldthwait's procedure, the patellar tendon was split into two vertical halves, and the lateral half of the tendon was detached from its tibial attachment. The lateral half of the patellar tendon was passed underneath the medial half and attached to the tibial periosteum using absorbable sutures. The thinned-out VMO was advanced and connected to the medial aspect of the patella and proximal tibia to maintain its medial pull on the patella. Subsequently, the semitendinosus tendon was harvested as a free graft for MPFL reconstruction. The patellar tunnel, parallel to the patellar articular surface, was drilled horizontally using a 4.5 mm drill bit. ST-free graft was passed through this tunnel, and the lateral tip of this graft was brought back on the medial side by passing over the anterior surface of the patella. The graft was secured onto the patella using Ethibond interrupted sutures over the medial and lateral aspects of the patella. The lateral end of the free graft was stitched onto the body of the graft. The medial end of the graft was passed through a soft tissue tunnel between the medial joint capsule and VMO. It was then passed under the adductor magnus tendon and sutured onto itself with 30 degrees of knee flexion using Ethibond.

Soft tissue balancing, patellar tracking, and knee ROM were assessed after every surgical procedure (Fig. 4). Layered closure was achieved, and an above-knee (AK) cylindrical POP slab was given.

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Fig. 4 Intra-op assessment of Patellar stability and tracking at 120° knee flexion.

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3 Results

In the study, a total of seven patients (four females and three males) were included for analysis. Their ages ranged from 4 to 9 years, with a median age of six years. Four patients had right knee involvement, while three patients had left knee involvement. One patient had Down Syndrome. The mean degree of flexion at which the patellar instability was noted was 20° (range 15°–30°). There were no cases of patella alta/baja. The surgical procedure had an average duration of 100 min. The average hospital stay for the patients was five days. The patients were followed up for 24 months, and their clinical and functional status was recorded at 6, 12, and 24 months post-operatively (Table 1).

Before the surgery, the mean Kujala score, which measures knee function and patellofemoral symptoms, was 55.85 ± 6.87. However, following the procedure, the mean score improved to 92.85 ± 2.64, which was highly significant (p < 0.0001) on a paired t-test, indicating positive outcomes. All patients reported a satisfactory functional recovery at six months post-operatively, and they could return to playing activities at 16 months post-operatively. One case had wound dehiscence after the surgery, which was managed with local wound care and secondary suturing. No reported complications, such as patellar fractures, infections, or recurrence of instability were observed in any of the cases. There was no FFD or extensor lag in any of the cases (Fig. 5).

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Fig. 5 No extensor lag following the surgery with restoration of full extensor power at 1 years post-op.

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4 Discussion

Patellar instability is an uncommon but disabling knee pathology with an incidence ranging from 6 per 100,000 in the adult population to 43 per 100,000 in the pediatric population.¹ The etiology of habitual and recurrent patellar instability can be traumatic or atraumatic. Atraumatic factors consist of Genu valgum or recurvatum, external Tibial torsion deformity, Trochlear/lateral condylar dysplasia or hypoplasia, increased Femoral anteversion, generalized ligamentous laxity, and syndromic conditions like Down's Syndrome, Turner's Syndrome, and William's Syndrome.^3–6 Pathological anatomical deviations in recurrent patellar instability includes lateral patellar retinacular tightness, subdermal fascial bands on the lateral aspect of the thigh, fibrosed vastus lateralis, deficient Vastus Medialis Obliquus (VMO), and torn/stretched out Medial Patello-Femoral Ligament (MPFL).

A key parameter in assessing patellofemoral stability is ‘Q-angle’, which is defined from the midpoint of the patella to ASIS and the tibial tuberosity. Historically, the initial treatment strategies for patellofemoral instability focused on distal realignment procedures aimed at correcting the Q-angle. The oldest documented surgical intervention was proposed by Roux, which involved tibial tubercle transfer; however, subsequently Goldthwait suggested the transfer of the lateral half of the patellar tendon to the pes anserinus. However, the clinical efficacy of these interventions addressing the lower ray of the Q-angle, as a stand alone procedure, has proven to be limited, and thus attention was drawn towards proximal limb of Q-angle.¹⁵ Insall's proximal “tube” realignment directed towards this theory; however, when performed in isolation, this technique has demonstrated suboptimal results.¹⁶ The inadequacy of this and other similar methodologies has been attributed to the non-anatomic nature of the repairs achieved.^10,17,18 To overcome these shortcomings and given the elusive, multifactorial etiology, Joo et al. combined the approach of proximal and distal realignment and advocated the 4-in-1 procedure for the first time in 2007.¹³ The initial 4-in-1 procedure consisted of Lateral release with V-Y plasty of Vastus lateralis, Insall's proximal tube realignment, modified Roux Goldwait procedure, modified Galeazzi's Semitendenosis tenodesis (Semitendenosus tendon is harvested while keeping its distal end intact. Tendon is pulled obliquely across the surface of the patella and fixed with metallic suture anchor in Patella).¹³ Subsequently, various modifications to this ideology has comeup in past, each aiming towards better and more anatomic outcomes. However, all previous modifications involved some compromise to the bony integrity or use of metallic implants. Bony procedures in open physis may result in growth disturbances or inadequate implant's purchase in early age group.

Medial patellafemoral ligament (MPFL) is most important static restraint for lateral patellar instability.¹⁹ Hence, MPFL reconstruction has also been explored for patellar instability. However, the recurrence rate following isolated medial patellofemoral ligament (MPFL) reconstruction in cases of habitual patellar dislocation is notably high, with studies indicating rates of 20 % reported by Lind et al., up to 20 % by Shamrock et al., and up to 38 % by Wilkens et al.^19–21 Various surgical techniques for MPFL reconstruction in the pediatric demographic have been proposed; however, many of these involve bony procedures with screw fixation, which may impair normal growth and lead to deformities resulting from hemiepiphysiodesis.^10,21,22 Two prevalent techniques for MPFL reconstruction utilizing a soft tissue pulley are the modified Chassaing Technique and Yercan's technique.^19,23,24 The modified Chassaing Technique, as explored by Lind et al.¹⁹ and Rabattu et al.,²³ incorporates the gracilis tendon, with aperture fixation employing two patellar tunnels and a soft tissue pulley affixed via the medial collateral ligament (MCL). However, this technique presents several disadvantages, particularly in the pediatric population, including the challenge of creating two tunnels with a significant risk of tunnel blowout, potential for iatrogenic patellar fractures, inadvertent MCL injuries, and the financial burden associated with aperture fixation implants. The advantages include easy localization of the adductor magnus tendon, reduced chances of iatrogenic injury to the pulley anchor since the adductor magnus tendon is mobile, and there is no need to split the anchor (unlike the MCL in the Chassaing technique). Additionally, there is no requirement for costly implants, and only one patellar tunnel is necessary.

Thus the authors of this current study developed a new modification to 4-in-1 procedure with Lateral release + VMO advancement + Modified Roux Goldwait procedure + MPFL reconstruction using Yercan's method.²⁴ The current all soft tissue surgical technique is not only reproducible, but is also cheap as it does not involve any implants like metallic staples or suture anchors as used in previous 4-in-1 procedures. The results of our novel technique have been compared with existing well-established 4-in-1 techniques. There was no significant difference in Kujala scores (p > 0.05) of Joo et al.¹³ and Danino et al.,²⁵ however, significantly better results were found in the current study as compared to the results of Malagelada et al.²⁶ Also, no recurrence was present in the current study at 3 years followup. In contrast, all three previous studies showed some cases of either subluxation or frank dislocation (Table 2).

Thus, the advantages of our novel technique includes, 1) This technique includes semitendinosus as a graft, which preserves the continuity of the extensor mechanism, 2) It does not require bony procedures, minimizing the risk of growth disturbances and iatrogenic fractures, 3) Cheap as compared to other techniques as it does not involve usage of any orthopaedic implants, 4) Easy localization of Adductor magnus tendon as compared to MCL in other techniques, 5) Restoration of primary static restraint for lateral patellar instability, i.e. MPFL, 6) No need of costly equipment like C-arm fluoroscopy.

Despite the effectiveness of our technique, it has a few potential disadvantages: 1) The tunnels created on the patella may enlarge, leading to patellar fracture and failure of graft fixation.²⁷ 2) Lateral retinacular release may lead to over-correction or iatrogenic maltracking of the patella.²⁸ 3) Some patients may develop symptoms of anterior patella-femoral stuffing.²⁹ Further research with a larger patient population and longer follow-up is necessary to improve the effectiveness of our technique.

5 Conclusion

Our study has demonstrated that using a 4-in-1 surgical technique for habitual patellar dislocation in children with open physis avoids bony procedures and combines soft-tissue procedures, and is effective in preventing further patellar dislocation in patients with habitual patellar dislocation. It is simple, cheap, and does not require any image guidance. However, careful surgical and post-surgical rehabilitation techniques have to be followed to prevent post-op complications.

Consent statement

Written informed consent has been obtained from the patient or guardian for participation and publication.

Author agreement

All authors read and approved the final manuscript.

Ethical considerations

The Institutional Ethics Committee and Institutional Review Board have reviewed the research protocol and manuscript.

CRediT author role in manuscript

IJ: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing - original draft; SB: Project administration, Investigation, Methodology, Writing - original draft; CS: Visualization, Project administration, Supervision, Investigation, Methodology, Writing - review & editing; MP: Visualization, Project administration, Supervision, Investigation, Methodology, Writing - review & editing; AJ: Writing - review & editing.

Financial support

The authors have no relevant financial or non-financial interests to disclose.