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Patellar Malalignment |
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Anatomy:Patellar increases quads power by 33-50%. Patellar articular cartilage is the thickest in the body – up to 7mm, does not directly follow contour of underlying bone, its apex is lateral to bony apex in 60%, the medial facet is concave, and the lateral facet is convex. Joint reaction forces are around 50% Body weight (BW) during normal walking, 300% BW climbing stairs and 800% BW in deep flexion. Force is dissipated such that force is greater in quads tendon than in patellar tendon. The patellar ossifies (appears on radiographs) around the age of three years. Patellar engages with the femoral trochelea at 20° of flexion. During flexion, from 10-90° patellar contact point moves from distal to proximal, 90-120° contact point moves back to near middle of patellar, > 120° there is no contact between medial facet and MFC. Operation Video Overview
Patellar dislocation (knee cap dislocation):This is a common injury mainly in young females with joint hyper flexibility. It used to be a difficult problem to manage. There have been many surgical and non-surgical techniques described aiming at treating this condition with variable level of success. Classification of patellar dislocation:
Traumatic and recurrent patellar dislocations:These two conditions are related and represent the majority of dislocations. Traumatic dislocation becomes recurrent in 15-45% of cases which occur in females more than males with a ratio of (2:1), and there is a familial association. Aetiology:Involves Bony factors such as increase femoral anteversion (Q angle), Patellar alta (high positioned patellar, hypoplastic lateral femoral condyle (congenitaly small size lateral femoral condyle), trochlea hypoplasia (shallow groove femoral trochlea), hypoplastic patellar (small size patellar), genu valgum (knocked knees), lateral position of the tibial tubercle and external tibial torsion (laterally rotated tibia). Soft-tissue factors include abnormality of vastus medialis obliqus muscle (VMO) either primary hypoplasia or secondary to trauma of the muscle, generalised ligaments laxity (this is very common), tight lateral restraints and medial patello-femoral ligament (MPFL) abnormality such as traumatic rupture. Patient usually presents acutely with pain, difficulty moving the knee and marked swelling. Clinical examination:During stance and walking, the patient may present with squinting patellar (patellar point in on standing due to femoral anteversion) or grasshopper patellar (patellar sitting high and lateral). Mal-tracking of the patellar is another important finding such as lateral subluxation of the patellar as the knee approaches terminal extension. Apprehension test is very useful in detecting subluxation, with knee at 30° flexion the patellar is pushed laterally, positive if there was apprehension or reflex quadriceps contraction. Also apprehension or reflex quadriceps contraction as the knee is slowly extended is regarded as a positive test. Another positive finding if the patient has the features of generalised ligamentous laxity; positive if 3 out of 5:any of the fingers hyperextension to parallel with the forearm, if the thumb can touch the forearm, elbow hyperextension, knee hyperextension and the ankle dorsiflex beyond 45. Radiological assessment:Plane radiographs can be very useful in making the diagnosis on standard skyline view the patellar will be laterally shifted and tilted. On the anteroposterior view, the patellar may be laterally positioned. On the lateral radiograph the patellar may be positioned higher than usual. Marked haemoarthrosis (blood collection if the joint cavity). MRI scan is very useful especially in the presence of recent dislocation. Many pathological findings could be diagnosed via MRI scan such as rupture of the MPFL, joint effusion (fluid such as blood in the joint), bruising to the medial patellar surface, bruising to the lateral femoral condyle where the patellar dislocate, the presence of loose bodies and other soft tissue, such as cartilage damage. Photos:
           Treatment:In the past, patellar dislocation used to be treated conservatively by close reduction then immobilisation in a brace healing up to 6 weeks including physiotherapy and rehabilitation. The rehabilitation program includes:
If conservative treatment failed and the patient kept complaining of pain or developed recurrent dislocations of the patellar then surgical management used to be the next step. There are more than 100 procedures described to treat this problem, which give the impression that there is no one proven technique to be the best in treating this pathology. Our approach:It is very common that there would be an intra-articular pathology associated with or resulted from patellar subluxation / dislocation. For that reason we believe that both plane radiograph and MRI scans are important to reach the appropriate diagnosis. If surgery is indicated then the best evidence based medicine suggests in principle that restoration of anatomy and early mobilisation provides the best outcome. We apply this principle by reconstructing of the MPFL that is ruptured (restoring anatomy). We use early rehabilitation starting the first week after surgery aiming at increasing the range of movement - over the first 6 weeks to more than 90 degrees of flexion and restoring the muscle strength within the same period. This type of aggressive rehabilitation could only be achieved by using a strong reliable graft such as the LARS ligament, which is strong enough to provide initial stability of the joint and a scaffold for the natural ligament to heal and grow back over the graft. We have been using this technique with a high success rate and minimal adverse outcome. This technique does not involve any major alteration to the patient’s anatomical structures, which makes it easy to perform any further surgeries in the future if need be. On the other hand traditional surgeries such as tibial tubercule osteotomy, patellar tendon transfer, VMO advancement and trochealioplasty all involve significant modification to the patient anatomy, which may make future surgery such as knee arthroplasty much more difficult and this may eventually lead to a poor outcome. Technique:We have modified a minimally invasive surgical technique to reconstruct the MPFL. The first part of the procedure includes knee arthroscopy to remove any loose bodies and deal with other intra-articular pathologies that may be associated with the injury. The second part of the procedure includes a minimally invasive open approach to the patellar. A 3-4cm vertical skin incision is made over the lateral one third of the patellar. Through this incision we perform a lateral release of the patellar and then under image intensifier guide a 5mm horizontal drill over a guide wire through the centre of the patellar. A patellar tendon type LARS ligament is then passed through the patellar drill hole from lateral to medial, using a special wire passer. The lateral end of the LARS ligament is sutured to the lateral edge of the patellar at the insertion site using number 2 fiberwire (strong suture) to prevent pull through the ligament. Usually the LARS ligament has a metal pin like an indo button, which adds stability to the structure. Using an image intensifier a second 1-2cm incision is made over the natural attachment of the MPFL. Using long forceps we create a tunnel in the soft tissue between the two incisions entering at the medial wound underneath the retinaculum and exiting at the first incision. The LARS ligament is then passed through this soft tissue tunnel. Under the image intensifier a second 5mm drill tunnel over a guide wire is made directed from the medial aspect of the femoral condyle at the natural insertion site of the MPFL. This is aimed at the anterolateral extra-articular corner of the distal femur exiting through the first wound. The LARS ligament is then passed through the second tunnel entering at the medial side and exiting at the anterolateral corner of the distal femur. This tunnel has to be accurately positioned in the epiphysis in the case of treating skeletally immature patients to avoid injury to the growth plate. The patient’s knee is then positioned at full flexion with the patellar fully engaged in the femoral trochlea. The LARS ligament distal end is gently tugged to avoid over loosening or over tightening then over a blunt guide wire a 6mm interference screw is inserted through the medial wound. The knee is then taken through a range of motions to check tracking and patellar stability. The distal end of the LARS ligament is then excised and final radiographs are taken. The wound is closed in layers and a bandage dressing is then applied with no need for a brace.
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