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Patellofemoral Realignment Surgery

Patellofemoral Malalignment and Instability

The patella is part of the extensor mechanism of the knee (quadriceps muscle) and functions to increase the strength and reduce the friction of the quadriceps muscle as it works across the knee. The patella articulates with the end of the femur in a tongue and groove arrangement. The groove on the end of the femur is called the femoral trochlea. The tongue in groove articulation between the patella and the femoral trochlea is affected by a number of factors, any combination of which can lead to problems with the way the patella relates to the femoral trochlea. In its milder forms, patellofemoral malalignment can cause pain at the front of the knee (anterior knee pain) and subsequently patellofemoral arthritis and in its more severe forms causes the patella to dislocate.

The Causes of Patellar Dislocation

As mentioned above a number of factors affect the way the patella relates to the femoral trochlea. A problem with one or more of these factors can cause the patella to maltrack and to dislocate. These factors include:

  1. Trochlear Dysplasia. Trochlear Dysplasia refers to femoral trochlea anatomy. In a normal situation the trochlea forms a deep groove of constant depth. Once the patella is engaged in this groove is it extremely difficult to dislocate. In Trochlear Dysplasia the groove is too shallow, particularly high in the groove in which case the trochlea does not adequately contain the patella until the knee is in deep flexion. This leaves the patella vulnerable to dislocation early in the knee flexion arc which is the position in which the foot strikes the ground when running.

  2. Patella Alta. Patella Alta means that the patella sits too high in relation to the femoral trochlea. As a result of this the patella does not properly engage the trochlea groove until the knee is in deeper flexion. As with Trochlear Dysplasia, Patella Alta leaves the patella vulnerable to dislocation early in the flexion arc. A combination of Patella Alta and Trochlear Dysplasia is an extremely potent one and is associated with a high risk of recurrent patellar dislocation.

  3. Medial Patellofemoral Ligament Insufficiency. The Medial Patellofemoral Ligament stops the patella dislocating in the first 20º of the flexion arc and is therefore particularly important in individuals with Patella Alta and/or Trochlear Dysplasia. A traumatic patellofemoral dislocation usually results in a rupture of the Medial Patellofemoral Ligament. This generally does not heal well and results in an increased risk of further dislocations, particularly in those with Patella Alta and/or Trochlear Dysplasia.

  4. Increased Quadriceps Angle. Quadriceps angle refers to the angle of divergence between the line of pull of the quadriceps and the line of pull of the patella ligament. The wider this angle the harder the quadriceps muscle will try to dislocate the patella when it contracts.

Other factors do affect patellofemoral instability but the four factors outlined above are critical with respect to treatment and surgical decision making.

Surgery for Patellofemoral Instability

In the past, all individuals with patellofemoral instability underwent similar surgery regardless of what anatomic problems were causing the patella to dislocate. The state of the art approach to patellofemoral instability is to precisely measure the affect of the four factors outlined above and to correct them as required. These factors are assessed with a clinical examination and with an xray, CT scan and MRI scan. Surgical treatment can then be individualized to correct any one individual's specific anatomic deficiencies. Frequently this will involve correcting two or three factors at the one time. Examples of patellofemoral surgery include:

  1. Medial Patellofemoral Ligament Reconstruction.  In an MPFL reconstruction the Gracilis tendon is harvested from the back of the leg through a small incision on the shin.  The gracilis tendon is doubled and fixed to bone tunnels in the patella and the femur.  The graft is tensioned so that the patella can no longer dislocate but is not pulled too hard against the femur.

  2. Tibial Tuberosity Osteotomy. A tibial tuberosity osteotomy is done to treat Patella Alta and/or an increased quadriceps angle.  The patella ligament runs from the patella to the top of the tibia.  Patella Alta is treated by moving the bony attachment of the patella ligament on the tibia distally (downwards) and an increased quadriceps angle is treated by moving the bony attachment of the patella ligament medially (inwards).  A combination of Patella Alta with an increased Q-angle is treated by moving the bony attachment both downwards and medially.
Fig 1. Patella Alta. Fig 2. Corrected by
distalizing osteotomy.
  1. Trochleaplasty. A trochleaplasty is a large and very invasive procedure that involves deepening a shallow femoral trochlea.  The only indication for a trochleaplasty is recurrent dislocation of the patella when the only identifiable problem with the knee is with the trochlea.  In most cases, Trochlear Dysplasia will be associated with either Patella Alta, an increased quadriceps angle, a Medial Patellofemoral Ligament insufficiency or a combination of these conditions and the treatment of these other three conditions is all that is required to control the patella.  Recurrent patellar instability in the context of isolated Trochlear Dysplasia is very unusual hence the infrequent need to undertake a Trochleaplasty.

  2. Lateral Release. Lateral Release is a procedure that historically is associated with patellofemoral instability surgery.  It is a destructive and painful procedure that adds greatly to the recovery time following surgery and is unnecessary in the vast majority of patients with a dislocating patella and is therefore rarely undertaken.

Recovery

Patellofemoral realignment surgery will involve admission on the day of surgery and either one or two nights in hospital depending on the scope of surgery undertaken. Restrictions on knee movement and weight bearing following surgery varies greatly depending on which procedure is undertaken. An isolated Medial Patellofemoral Ligament reconstruction, for example, requires no restriction of motion or weight bearing or generally have only a short timeframe on crutches. In contrast, a distalizing tibial tuberosity osteotomy requires six weeks of knee splintage, restrictions in how the knee is moved, weight bearing allowed only with the knee straight and a longer period on crutches. Physiotherapy and early postoperative treatment is geared to towards reduction of pain and swelling and rapid recovery of muscle control. Instruction in the home exercise program is given in hospital. A structured physiotherapy program is initiated within a week or two of surgery. The time frame for full recovery varies from three to six months depending on the extent of the surgery undertaken.

Risks and Complications

As with any major surgery, there are potential risks involved. The decision to proceed with the surgery is made because the advantage of surgery outweighs the potential disadvantages.

It is important that you are informed of these risks before the surgery takes place. Complications can be general medical complications or local complications specific to the knee.

Patellofemoral realignment surgery is usually undertaken on young healthy individuals and general medical complications are uncommon but possible. Complications include:

  • Allergic reactions to medications
  • Side effects to painkilling medications such as nausea and vomiting
  • Pneumonia

Local complications:

  • Infection. Infection can occur with any operation in the knee.  This can be superficial or deep.  Infection can have very serious consequences and may require a re-admission to hospital and further surgery.

  • Blood Clots (Deep Venous Thrombosis). These can form in the calf muscles and travel to the lung (a pulmonary embolism).  These can occasionally be serious and even life threatening.  Any calf pain or shortness of breath in the early postoperative period should be notified immediately.  The key to avoiding DVTs is mobility.  It is not so much the time spent mobilizing but the frequency of mobilization that is important.  In the early postoperative period a lot of small movements is the best prevention.  Other prevention strategies will be employed and individualized to the patient.

  • Stiffness. The aim of patellofemoral realignment surgery is to produce a stable knee without restriction of movement.  Loss of movement following patellofemoral realignment surgery is very uncommon but control of swelling and attention to home exercise program and physiotherapy appointments is an important part of regaining full movement as early as possible.

  • Nerve Injury. Patellofemoral realignment surgery is not particularly threatening surgery to any major nerves.  A small nerve that crosses just below the insertion of the patellar tendon on the tibia is routinely cut and results in numbness in the upper outside part of the calf.  Most people are very aware of this numbness early on but the sensation tends to fade with time.

  • Recurrent Instability. Further dislocations following instability are a rare event but are possible if enough force is applied to the joint.
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