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P&P #70: Treatment of Knee Conditions

The treatment of knee conditions such as chondromalacia patellae by leg extension exercises to alter 'muscle balance' may be based on faulty or doubtful premises.

Treatment of the condition involving deterioration of the articulating surface beneath the patella (often referred to as chondromalacia patellae - CPAT) is usually based on the premise that some muscular imbalance between vastus medialis and vastus lateralis causes the patella to track imprecisely over the femur.

Apparently, a weaker v medialis relative to the v lateralis permits the patella to be pulled laterally out of its most efficient trajectory over the femur, thereby leading to uneven wear of the cartilagenous bearing surface beneath the patella.

Consequently, therapists have tried to strengthen the v medialis with knee extension exercises on isokinetic dynamometers or with various forms of electrostimulation (faradism, interferentialism or so-called 'Russian stimulation') in an attempt to improve the medialis/lateralis strength ratio. Many clinical and theoretical studies have attested to its success and validity, but the underlying mechanical process might not be as clearcut as has been suggested.

The traditional explanation of strengthening v medialis implies that strengthening of this muscle causes the patella to be 'pulled in' closer to its 'ideal' trajectory during any movement which involves significant knee flexion. A simple geometric analysis of the situation implies further that :
  1. v medialis must then shorten more than it did before treatment; or
  2. v medialis has been shortened chronically by the treatment.
If either of these implications is correct, then there must be some evidence either that training causes any given muscle to contract to a greater extent than the same unexercised muscle or that extended range training causes a muscle to shorten progressively. If this suggested analysis is incorrect, then another possible explanation has to be sought, possibly in altered neuromuscular control or kinaesthetic processes.

This does not deny the fact that this type of therapy often may diminish peripatellar pain and improve knee extension strength, but it serves to point out that some of the traditional rationales for this type of injury management may not be correct or as simple as are implied by the current theories.

This analysis may also have profound implications for the entire concept of testing and training muscles to enhance performance, facilitate rehabilitation or prevent injury. In trying to understand the relevance of muscle ratios, we have to search for rational hypotheses in structural, functional or combined (structural-functional) processes.

For instance, has it been proved beyond a shadow of doubt that 'muscle imbalances' are a major cause of injury or impaired performance? Or is the cause of any problem rather to be sought in inappropriate patterns of muscle recruitment, irrespective of the balance between the strength of any muscles involved? In other words, is the dominant cause of injury or impaired performance due more to neuromuscular control or motor skill factors than 'muscle imbalances'?

Moreover, in attempts to analyse muscle balance and imbalance, how solid are the current norms against which these balances are measured? We also have to examine differences in muscle balance under static or static stabilising conditions, as well as under dynamic conditions at different velocities and in different patterns of cocontrative and ballistic action.

We cannot simply assume that balance under dynamic conditions implies equal balance under explosive, slower or static conditions. Is this type of biomechanical analysis carried out yet with this degree of thoroughness or are therapists quite blindly extrapolating fixed path analysis on an isokinetic dynamometer to all other multi-dimensional stabilising and moving conditions to be encountered by the athlete? If the latter, why do therapists continue to use such a flawed and dubious method of treatment and assessment?

So, our critical analysis of the idea of an idealised perfect patella trajectory under 'balanced' muscle action has led us to re-examine the entire concept of testing and rehabilitation based on machine measurement under very rigid mechanical conditions.

Comment on the current explanations for the validity of CPAT rehabilitation and on the general concept of specific, fixed muscle balances concerning all other joints in the body. The validity of extrapolating machine testing to sports functional performance may also bear some critical analysis.


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