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Medial knee with patellar and femoral fixation of a gracilis graft for recurrent lateral patellar instability | intermediate

Surgical Imaging

Imaging Gallery

Arthroscopic view of the medial knee with the patella, MPFL and medial femoral condyle labelled — Arthroscopic view of the medial compartment demonstrating the patella (top), the medial patellofemoral ligament (MPFL) running to the medial patellar border, and the medial femoral condyle (Femur, below). The MPFL is the primary passive restraint to lateral patellar translation in the first 0-30 degrees of flexion.Credit: Kodkani PS et al. via Open-i (NIH), PMC4759872 (CC BY)

Intraoperative photo showing two small medial incisions used for minimally invasive MPFL reconstruction — Minimally invasive MPFL reconstruction performed through two short incisions - one over the medial border of the patella and one over the medial femoral epicondyle - through which the tendon graft is passed and tensioned.Credit: Kodkani PS et al. via Open-i (NIH), PMC4759872 (CC BY)

Intraoperative open view of graft fixation at the medial patellar border during MPFL reconstruction — Intraoperative open view during MPFL reconstruction with the medial soft tissues retracted to expose graft fixation at the medial border of the patella (basket-weave docking technique).Credit: Kodkani PS et al. via Open-i (NIH), PMC4759872 (CC BY)

Intraoperative photo of graft passage and femoral-side fixation at the medial femoral epicondyle — Intraoperative photograph showing graft passage and femoral-side fixation at the medial femoral epicondyle - the step at which accurate placement at Schottle's point determines graft isometry and final outcome.Credit: Krishna Kumar M et al. via Open-i (NIH), PMC4175865 (CC BY)

Critical Danger Structures

Danger 1: Saphenous Nerve (Infrapatellar Branch)

Infrapatellar branch of the saphenous nerve and the saphenous nerve in the adductor canal region. Location: crosses the medial knee superficially, vulnerable during the medial incisions and graft tunnelling between the patellar and femoral sites. Protection: keep dissection in the correct plane on the medial retinaculum, pass the graft deep to fascia (layer 2) and avoid blind subcutaneous tunnelling. Injury causes a painful neuroma and medial/anteromedial numbness.

Danger 2: Femoral Tunnel Malposition

Non-anatomic femoral fixation point. Location: the femoral footprint near the adductor tubercle and medial epicondyle; Schottle's point is the validated target. Protection: place the guidewire under fluoroscopic control on a true lateral and check graft isometry before fixation. A tunnel placed too proximal/anterior over-tensions the graft in flexion, causing stiffness, anterior knee pain, and medial patellar facet cartilage overload.

Danger 3: Graft Over-Tensioning

Excessive graft tension. Location: at final fixation, set with the knee in 30-60 degrees of flexion. Protection: the MPFL is a checkrein, not an isometric tether - secure with the patella centred and confirm at least one quadrant of passive lateral glide remains and that full flexion is achievable. Over-tensioning produces medial overload, loss of flexion, and recurrent anterior knee pain; under-tensioning permits recurrent instability.

Danger 4: Patellar Fracture / Articular Penetration

Patellar bone tunnels or anchors. Location: superomedial border and proximal half of the medial patella. Protection: keep tunnels in the proximal half, do not exceed roughly 4.5 mm diameter or breach the anterior cortex, avoid full-width transverse tunnels, and angle drills away from the articular surface. Tunnels weaken the patella and risk intra-operative or post-operative (often low-energy) patellar fracture and articular penetration.

Danger 5: Medial Femoral Condyle Articular Cartilage

Distal femoral articular surface adjacent to the femoral tunnel. Location: the medial femoral condyle articular cartilage lies close to the femoral footprint and the trochlea if trochleoplasty is added. Protection: aim the femoral tunnel guidewire distally and anteriorly away from the joint and the intercondylar notch, confirm position on imaging, and protect the cartilage during interference screw insertion. Injury accelerates patellofemoral and tibiofemoral degeneration.

Mnemonic

BONEBONE - The Four Bony Risk Factors to Measure Before MPFL Reconstruction

Mnemonic

GRAFTGRAFT - Operative Sequence for the Reconstruction

Primary Indications

Absolute Indications

Recurrent lateral patellar dislocation (two or more episodes) with a torn or incompetent MPFL
Objective instability with positive apprehension and a J-sign, confirmed MPFL disruption on MRI
Failed structured non-operative management (bracing, physiotherapy focused on VMO and hip abductors, activity modification)
Recurrent instability following a first dislocation associated with an osteochondral fragment or significant risk factors

Relative Indications

First-time dislocation with a displaced osteochondral fracture requiring fixation, where MPFL is addressed at the same sitting
High-demand athlete with persistent functional instability despite rehabilitation
Instability in the presence of correctable bony risk factors, where MPFL reconstruction is combined with bony procedures (a la carte)
Persistent instability after prior lateral release or distal realignment without medial reconstruction

Contraindications

Active infection overlying or within the knee
Established patellofemoral osteoarthritis where reconstruction may worsen medial overload (relative)
Uncorrected major bony abnormality where MPFL reconstruction alone will predictably fail (e.g. high-grade trochlear dysplasia, grossly elevated TT-TG, marked patella alta) without addressing the bone
Skeletally immature patient with open physis - femoral fixation must avoid the distal femoral physis (use a physeal-sparing technique)
Painful maltracking without true instability (a wrong diagnosis - reconstruction will not help patellofemoral pain alone)

Bony Risk Factors - Measure Before You Operate

MPFL reconstruction restores the soft-tissue checkrein but does not change the bone. The classic risk factors (Dejour) must be quantified pre-operatively.

TT-TG Distance (tibial tubercle-trochlear groove)

Measured on superimposed CT or MRI axial slices; quantifies lateralisation of the extensor mechanism
Normal is roughly less than 15 mm; greater than 20 mm is abnormal and an indication to consider a medialising (and/or distalising) tibial tubercle osteotomy
Values of 15-20 mm are a grey zone judged alongside other factors

Trochlear Dysplasia (Dejour classification)

Type A: shallow trochlea, crossing sign on lateral, sulcus angle preserved enough for MPFL alone in many cases
Type B: flat or convex trochlea with a supratrochlear spur (crossing sign plus spur)
Type C: asymmetry of the facets with a double-contour sign, medial facet hypoplasia
Type D: features of B and C combined - spur plus cliff/double contour, the most severe ("cliff pattern")
High-grade dysplasia (B-D), particularly with a prominent supratrochlear spur, is the indication to consider sulcus-deepening trochleoplasty

Patellar Height (patella alta)

Caton-Deschamps index (patellar articular surface length related to articular surface-to-tibial plateau distance): greater than 1.2 defines alta
Insall-Salvati ratio (patellar tendon length / patellar bone length): greater than 1.2 suggests alta (less than 0.8 suggests baja)
Alta delays engagement of the patella in the trochlea, prolonging the unstable arc, and may warrant distalising tubercle osteotomy

Evidence Base

The key technique and outcome claims of this operation rest on a small, well-defined evidence base spanning the biomechanical role of the MPFL, the radiographic landmark for femoral placement, the bony risk-factor thresholds, the complication profile, and the rationale for combined bony procedures.

Radiographic landmarks for femoral tunnel placement in MPFL reconstruction

Schottle PB, Schmeling A, Rosenstiel N, Weiler A • Am J Sports Med

Clinical Implication: Provides the validated intra-operative target (Schottle's point) for femoral tunnel placement - the single most important technical determinant of outcome. Drilling on a confirmed true lateral, not surface anatomy, is mandatory.

Verify on PubMed (PMID 17267773)

Location of femoral attachment and length-change patterns of anatomic versus nonanatomic MPFL attachments

Stephen JM, Lumpaopong P, Deehan DJ, Kader D, Amis AA • Am J Sports Med

Clinical Implication: Explains why a proximal or anterior femoral tunnel over-tensions the graft in flexion (loss of flexion, medial overload) - the basis for the on-table length-change check before drilling.

Verify on PubMed (PMID 22729504)

Evaluation of the medial soft-tissue restraints of the extensor mechanism of the knee

Conlan T, Garth WP Jr, Lemons JE • J Bone Joint Surg Am

Clinical Implication: Establishes the MPFL as the principal medial restraint (roughly half the restraining force) and the logical reconstruction target after lateral dislocation.

Verify on PubMed (PMID 8501083)

Factors of patellar instability: an anatomic radiographic study

III

Dejour H, Walch G, Nove-Josserand L, Guier C • Knee Surg Sports Traumatol Arthrosc

Clinical Implication: Source of the numeric thresholds examiners expect (TT-TG 20 mm, Caton-Deschamps 1.2) and the rationale for measuring and correcting bony pathology - MPFL reconstruction alone does not change the bone.

Verify on PubMed (PMID 7584171)

Systematic review of complications and failures of MPFL reconstruction for recurrent patellar dislocation

Shah JN, Howard JS, Flanigan DC, Brophy RH, Carey JL, Lattermann C • Am J Sports Med

Clinical Implication: Quantifies the complication burden and identifies technical error (especially femoral malposition) and patellar fracture as key avoidable failure modes - directs prevention and counselling.

Verify on PubMed (PMID 22679297)

Combined trochleoplasty and MPFL reconstruction for recurrent dislocation in severe trochlear dysplasia

Nelitz M, Dreyhaupt J, Lippacher S • Am J Sports Med

Clinical Implication: Supports the a la carte principle: in high-grade (Dejour B-D) dysplasia, adding trochleoplasty to MPFL reconstruction reliably restores stability where isolated soft-tissue surgery would risk failure.

Verify on PubMed (PMID 23467555)

Clinical Decision Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"A 19-year-old netball player has had three lateral patellar dislocations over two years. MRI confirms an MPFL rupture. CT shows a TT-TG distance of 22 mm, Caton-Deschamps index of 1.1, and Dejour type A trochlear dysplasia. She has failed a structured physiotherapy programme. How would you manage her, and what determines whether MPFL reconstruction alone is enough?"

PRACTICAL APPROACH

This young athlete has objective recurrent lateral patellar instability with a confirmed MPFL rupture and has failed appropriate non-operative management, so she has a clear indication for surgical stabilisation. Before deciding on the operation I must characterise her bony risk factors, because MPFL reconstruction is a soft-tissue checkrein that restores the primary restraint in early flexion but does not change the bone. I would confirm the measurements: her TT-TG distance is 22 mm which is abnormal (greater than 20 mm), her Caton-Deschamps of 1.1 is within the normal range so she does not have significant patella alta, and she has only low-grade (Dejour A) trochlear dysplasia. The key decision is the a la carte approach popularised by Dejour - individualise the operation to the measured pathology. Her trochlear dysplasia is low grade so she does not need a trochleoplasty, and her patella is not alta so she does not need distalisation. However her TT-TG of 22 mm is elevated, which means MPFL reconstruction alone risks leaving an excessive lateralising vector on the graft. I would therefore plan an MPFL reconstruction combined with a medialising tibial tubercle osteotomy to bring the TT-TG into the normal range and protect the reconstruction. Technically I would harvest a gracilis autograft, fix it to the proximal half of the medial patella, identify the femoral point using Schottle's landmark on a true lateral radiograph, confirm length-change behaviour before drilling, and tension the graft at 30 to 60 degrees of flexion as a checkrein with the patella centred, preserving full flexion and about one quadrant of lateral glide. I would counsel her that addressing both the soft tissue and the bony lateralisation gives the best chance of preventing recurrence, and that return to netball is typically around four to six months once strength and control criteria are met.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"Talk me through how you place the femoral tunnel in MPFL reconstruction, and why it matters so much. What is Schottle's point and how do you confirm your position is correct on the table?"

PRACTICAL APPROACH

Femoral tunnel position is the single most important technical determinant of outcome in MPFL reconstruction, because the femoral attachment governs the length-change behaviour of the graft through the flexion arc. The native MPFL is near-isometric - tightest in extension and early flexion and relaxing as the patella engages the trochlea past about 30 degrees. If I place the femoral tunnel correctly the graft reproduces this behaviour; if I place it too proximal or anterior the graft becomes tighter as the knee flexes, which over-tensions it, causes loss of flexion, medial facet cartilage overload and pain, and is the commonest avoidable cause of failure. Schottle's point is the validated radiographic landmark for the femoral insertion, defined on a perfect true lateral radiograph with the posterior femoral condyles superimposed. It lies approximately 1 mm anterior to the line of the posterior femoral cortex, about 2.5 mm distal to the posterior origin of the medial femoral condyle, and proximal to the level of the posterior point of Blumensaat's line. I obtain that true lateral under the image intensifier first, because an imperfect lateral makes the landmark meaningless. To confirm my position on the table I place a guidewire at Schottle's point and check it on the true lateral image. I then perform a length-change or isometry check: I loop a suture from the patellar fixation around the guidewire and take the knee through a full flexion-extension arc. Anatomic behaviour is that the construct is tightest near extension and relaxes or stays near-constant into flexion. If the suture tightens as the knee flexes, the point is too proximal or anterior and I reposition the wire before I drill. Only once both the radiographic position and the length-change behaviour are correct do I drill the femoral tunnel, aiming distally and anteriorly away from the articular surface and the notch.

CLINICAL SCENARIOStandard

CLINICAL PROMPT

"What are the main complications of MPFL reconstruction and how do you avoid them? A patient returns six weeks after surgery with recurrent lateral subluxation and a positive apprehension sign - what has gone wrong and how do you investigate?"

PRACTICAL APPROACH

The important complications cluster into technical errors and patient-factor failures. The commonest technical error is femoral tunnel malposition, which over-tensions the graft and causes loss of flexion, medial overload, or recurrent instability - prevented by using Schottle's point and a length-change check before drilling. Graft over-tensioning is the related error, avoided by tensioning at 30 to 60 degrees with the patella centred as a checkrein, confirming about one quadrant of residual lateral glide and full flexion. Patellar fracture is uncommon but serious; I reduce the risk by keeping patellar tunnels in the proximal half, using a modest diameter, not breaching the anterior cortex and avoiding a full-width transverse tunnel. Saphenous nerve and infrapatellar branch injury is avoided by careful dissection and passing the graft in the correct layer 2 plane, and arthrofibrosis is avoided by correct tensioning and early protected motion. Recurrent instability or graft failure is the failure that most concerns this patient. The two questions I always ask are whether the femoral tunnel was anatomic and whether the bony risk factors were addressed. Recurrence at six weeks with a positive apprehension sign suggests either a non-anatomic or too-distal femoral tunnel that never restored the checkrein, fixation failure, or - very commonly - an untreated bony abnormality such as high TT-TG, patella alta, or high-grade trochlear dysplasia that overwhelmed an isolated soft-tissue reconstruction. To investigate I would re-examine the knee documenting the direction and degree of instability and the J-sign, and compare with the other side. I would obtain plain radiographs including a true lateral and skyline views to assess patellar height, trochlear morphology and tunnel position, and a CT or MRI to remeasure the TT-TG distance, patellar height (Caton-Deschamps), trochlear dysplasia grade, and to confirm the femoral tunnel relative to Schottle's point and check the integrity of fixation. The findings then dictate revision strategy - correcting tunnel position and adding the appropriate bony procedure, a tubercle osteotomy and/or trochleoplasty, that was originally omitted.