Patella maltracking and instability can be quite disabling, requiring surgery to reposition and stabilise the patella to allow it to travel in a more normal manner and avoid episodes of subluxation and dislocation.
The patella or knee cap is a small but very important bone which actually endures more force across it than any other bone in the human body. It also travels up and down the knee in a relatively narrow groove known as the trochlea, and as a result of these two factors is susceptible to wearing out of the articular cartilage (arthritis) and also to developing an abnormal pattern of movement whilst remaining in the groove (maltracking) and/or instability by sliding partially (subluxation) or jumping totally (dislocation) out of the groove. Females are more at risk in general than their male counterparts for patellofemoral dysfunction because of their anatomical differences in pelvic shape, usually being slightly wider than the male pelvis and as a result the female knee is slightly more valgus or “knock knee” than the male knee. As the knee becomes increasingly “knock kneed” or V-shaped, an increased outwards force on the knee cap develops, the same way that a bow and arrow works, with increased pulling on the bow increasing the V-shape whilst at the same time increasing the pulling force on the arrow. Eventually, the force is strong enough to pull the knee cap (arrow equivalent) out of its normal resting position and this is one of the key contributors to patellofemoral maltracking and instability. Other factors that usually prevent the patella from subluxing or dislocating include the articular contours of the patella and the trochlea groove being a matching U or V shape, and if the patella or trochlea groove are shallow or flat (dysplastic) or small in size (hypoplastic), then it is easier for maltracking or instability. Sometimes patients have a patella which is tilted laterally and/or shifted slightly laterally (subluxed) with tight soft tissue restraints on the outside of the patella (lateral retinaculum) which can result in excessive force being applied to the outer half of the patella (lateral facet) and underlying trochlea groove, leading to local wearing of the cartilage and inflammation and pain, sometimes referred to as lateral patella pressure syndrome. Additionally, if patients have very lax or stretchy ligaments with an ability to hyperextend their joints, or they have had trauma or a dislocation with possible tearing of some of the normal restraints (medial patellofemoral ligament and medial retinaculum), or a patella which is located a bit “higher” than normal by being further away from the knee joint (patella alta) or by being more medially located than normal resulting in a “squinting” appearance of both knee caps and a sharper more acute angle (Q-angle) between the tendons above (quadriceps tendon) and below (patella tendon) the patella as it inserts into the bony prominence (tibial tuberosity) on the tibia, then they are at increased risk for maltracking and instability. Maltracking is usually subtle and occurs with every knee bend whereas instability (subluxation / dislocation) usually is quite dramatic and sporadic, and influenced by doing a particular activity, and may spontaneously reduce by itself or may require assistance to put the knee cap back in its correct position.
Assessing Options for Treatment
Repeated episodes of maltracking or instability predispose the knee to developing “wear and tear” of the cartilage on both the patella and trochlea groove (“chondromalacia patella”) and eventually to arthritis. If patients have these conditions and they are symptomatic, it is usually helpful to have a thorough assessment of their predisposing factors (anatomy of the knee as well as the hips and feet, lower limb alignment, ligamentous laxity, previous injuries or surgery) and where possible to institute a co-ordinated program of physiotherapy. Physiotherapy is tailored to the individual complaint, but in general includes stretches, strengthening, strapping, proprioceptive drills where patients are taught to be aware of where their knee cap is at any one time and activity modification with at risk activity avoidance. The most at risk position for patella dislocation is usually when the knee goes from being fully extended or out straight, into a knee bent position whilst the foot is planted on the ground and the body is turning away from the involved knee towards the other knee. If necessary other modalities such as patellofemoral bracing with a knee orthosis and/or addressing relevant foot pathology (flat feet/pes planus) with podiatry/orthotics may be necessary. If patients have only had one or two episodes of instability, they do not normally need surgery but if the predisposing factors are excessive or resistant to physical modalities, and the maltracking or instability continues to recur, then surgical intervention may be appropriate and careful consideration of the patients age and pathology will determine whether patients are in need of patellofemoral realignment and or stabilisation procedures and which specific (soft tissue and or bony) techniques to employ.
When Patella Realignment Surgery is the Best Option
When surgery has been decided as the best remaining treatment option, the patient’s age and specifically their skeletal maturity is assessed, to determine if the bones surrounding the knee joint are still growing with “open growth plates” or not. If the patient is young with open growth plates then surgery is restricted to a soft tissue procedure, in order to avoid premature closure of the growth plates and possible shortening or angular deformity of the knee and lower limb. Releasing tight tissue constraints laterally using a technique known as a “Lateral Release” which can be performed through a small 1cm keyhole incision with arthroscopic technique and/or in combination with an open reconstructive procedure. Often a medial sided tightening procedure is performed through a 3 fingerbreadth (5-6cm) longitudinal incision just above the patella with a VMO advancement, where a portion of the quadriceps tendon (VMO – Vastus Medialis Oblique) is detached from the patella and advanced before reattaching back onto the patella, and/or a repair of the medial ligaments and capsular attachments (MPFL – Medial PatelloFemoral Ligament) with tightening of the attachments onto the patella, and or augmentation with reconstruction of the MPFL using one or two of the patients hamstring tendons, which are weaved together and attached to the medial margin of the patella and back onto the femur, providing a strong restraint to further lateral subluxation /dislocation. If patients have achieved skeletal maturity and have an elevated “Q-angle” then additional bony surgery, with a tibial tuberosity osteotomy (TTO) is often employed through a 3 fingerbreadth (5-6cm) longitudinal incision below the patella, alongside where the patella tendon attaches to the tibia. Less commonly if patients have a flat or abnormally shaped (hypoplastic/dysplastic) trochlea groove, consideration of some form of trochleoplasty, where the flat groove is elevated and bone grafted underneath to allow for better tracking of the patella and resistance to sideways movement, to discourage future subluxations and dislocations. Following ligament reconstruction or osteotomy surgery a period of at least 4 weeks and more usually 6 weeks using of a range of motion brace and crutches is required, with increases each week in weight bearing and knee bending until regaining full weight bearing and range of motion. It is usually 3 months before patients are able to do some resisted strengthening exercises in the gym and by the 4 month mark, some sports specific training and usually returning to more vigorous activities by the 6 month mark.