The truth about jumping biomechanics and patellar tendinopathy (and more)

Hi all

Welcome to tendinopathy blog 3. One of my favourite topics in jump biomechanics and patellar tendinopathy, as well as a study investigating an ankle foot orthotic and tibialis posterior. As well as this have managed to sneak in two very interesting studies looking at calf muscle fascicle function with some interesting rehab implications.

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Van der Worp et al. have conducted a prospective study investigating landing biomechanics and jumper’s knee. The authors cite a review suggesting landing with a stiff knee strategy is associated with PT – it must be made clear that 1) this is data from one study (Edwards 2010) and 2) it was during a horizontal landing (eccentric phase) prior to a vertical jump, as in a spike jump (see figure below). In my recent free physioedge talk (you can listen here) I highlight the less than clear relationship between jump biomechanics and patellar tendinopathy. Key findings were 1) people with painful PT shift load away from the knee (may or may not have a stiff strategy) and may compensate with movement at other kinetic chain segments in an effort to dissipate load and maintain performance; 2) there were examples of poor calf and hip strategies, and a stiff knee strategy in horizontal landing (as mentioned above), and these may be risk factors.

Back to this featured study -  the authors recruited 49 korfball, volleyball and basketball athletes, 32 men, 17 women. They performed 2 leg drop jumps from 30cm followed by a maximal vertical jump, kinematics and force plate data were measured. Strangely they had the force plates positioned at half the participants height away from the step – so it was like a horizontal stop jump, only off a step. Only 3 athletes developed PT (2 male basketball, 1 female korfball athlete) so they described differences in their kinematics to the male or female norm groups, rather than performing stats. They found that leg stiffness of the injured group was within the highest 2 quartiles of the gender relevant norm group. Careful now in interpreting this – leg stiffness (GRF/leg displacement) is different to knee stiffness (knee torque/angular displacement). So makes sense as means they either had higher GRF or less leg displacement, both potentially increasing tendon load. What to do about it is the difficult thing as optimising leg stiffness is related to performance. Regarding kinematics, the injured female had greater hip flexion at initial contact (IC); and had less hip flexion total range; one of the males had excessive dorsiflexion and landed on their heel at IC – these patterns may reduce hip and ankle load absorption and increase knee load. The third subject had no major kinematic differences to the norm group. The authors quite rightly state multiple landing patterns may be related, influenced by individual factors such as muscle capacity, activation, flexibility, training, habit, sport, etc. And for some athletes, biomechanics may not be as relevant as other risk factors. Hats off the the authors for attempting a prospective study, but it does show that really large numbers are needed.

Christopher Neville and team have a study investigating a new ankle foot orthoses (AFO) in Posterior Tibial Tendon Dysfunction. This condition is associated with “collapse of the medial arch of the foot, abnormal forefoot abduction, and heel-rise weakness.” “Progression of PTTD is most commonly described as having 4 stages (I- IV). Stage I is defined as pain with no foot deformity, stage II as pain with a flexible flatfoot deformity, stage III as pain with a fixed flatfoot deformity, and stage IV as the progression to arthritic signs on the lateral foot with fixed flatfoot deformity. Stage II flexible flatfoot deformity is defined by the ability to passively place the foot in a neutral foot posture and by the presence of excessive rearfoot eversion, forefoot abduction, and a lower medial longitudinal arch.” They tested a lateral extension component vs standard AFO (see figure below) to see if this can better control the forefoot abduction component of PTTD stage II. 15 participants walked with each of the AFO’s + shoes, and with shoes only, in a random order and 3D foot motion was assessed. The main kinematic finding was that the AFO with lateral extension resulted in greater forefoot adduction (less abduction) compared to the standard AFO and the shoe only condition – 2.6 degrees improvement compared with the standard AFO which was just above measurement error, and 4.1 degrees compared with shoe only. The thought is this may change tibialis posterior load and symptoms. A consideration for these patients but also important to remember that good quality progressive strengthening does have a great deal to offer PTTD patients.

Interesting study but Butlet et al. of gastrocnemius architecture in relation to function. They suggest there may be gastroc architecture variation between populations that are specific to ecological and environmental demands – this is termed ecomorphology and is central to the studying evolution of primates. They found longer fiber lengths among a Ugandan hunter gatherer population. These populations climb trees a lot, mainly by hyper dorsiflexion (up to 45 degrees) as seen in the figure below. Ie they are adapted for greater joint excursion by having greater fascicle lengths. This contrasts to the short fibre lengths, greater pennation angles and high physiological cross sectional (PCSA) area in industrialised populations (Ward 2009, Lieber 2011 – this second one is a great read). PCSA takes into account muscle mass and pennation angle and is the best indicator of maximal muscle force – so the thought is industrialised populations are more suited force production rather than joint excursion. The authors also discuss how moment arm influences fiber excursion. Large moment arm means there is greater muscle tendon excursion for a given joint movement – so if a muscle is designed for force production with short fascicle lengths and a large PCSA (e.g. soleus), then fascicles may be compromised if there is large joint excursion, unless it has a relatively compliant tendon (yes), or small moment arm (variable). Soleus functions relatively isometrically in locomotion thanks to the compliance of the Achilles. Other muscles, like the hamstrings and gluteus maximus, have longer fascicle lengths and can cope with greater joint excursions and less compliant tendons. Important implication for tendon rehab is (drum roll please)…think about how the muscle fascicles function when prescribing rehab.

Interesting study by Kudo et al. They looked at fascicle length changes in the gastrocnemius during calf raises performed slow (1 per second) vs faster (1.5 per second) and to flat ground vs over a step. They found that the tendon stretched more and fascicle lengthening was less in the over the step phase of the calf drop – indicating that the gastrocnemius is acting almost isometrically in this phase, as it does in walking and running function. The authors argue that training over a step may therefore have better transfer to walk/run function – but of course clinically we need to beware of contraindications to over the step loading eg tendon and joint compression.