As a nonweightbearing sport (at least with road bicycling), it is common to assume that weightbearing types of problems would not occur. Although this is generally true, bicyclists develop conditions similar to weightbearing ones, but with different mechanisms of injury. Some common knee problems include: chondromalacia, or patellofemoral arthralgia; patellar and quadriceps tendinitis; medial shelf-plica and medial patellar tibial ligament irritation; and less commonly, biceps tendinitis. Many of these problems have similar biomechanical contributions. These include:
- riding in too high of a gear
- too slow of a cadence
- too low of a seat
- hill work
- excessive sprinting, or
- anatomic variants that place stretch or compression on specific knee structures
How these factors relate to specific conditions and the modifications available will be discussed. In general, increase stress to the quadriceps and patella are produced by too low a seat and too much resistance to pedaling. Compressive and shearing forces to the patella increase with more knee flexion. This is analogous to performing a squat. Using a high gear is analogous to increase the weight lifted with a squat position. Relatively, the same thing occurs with a seat position that is too far forward, forcing more knee flexion.
Anatomic variation may play a significant role in the development of overuse conditions. Excessive pronation, internal or external tibial torsion, and excessive varus and valgus knee angulation may produce increased stress at the knee. For example, the combination of pronation and internal rotation increases medial knee stress. This is of course also true in the weightbearing athlete, however it is often not considered in the bicyclist. Compensations for these variations can be accomplished through adaptations of the pedaling system. Here are examples of possible approaches to accommodation for specific anatomic variants:
- If the cyclist's foot is pronating, cycling orthotics may be prescribed. This type of orthotic is generally more rigid than running orthotics and extends support farther to include the metatarsal heads.
- If the cyclist has an increased valgus angulation to the knee, cants or lifts can be placed between the shoe and the pedal, which lifts the medial aspect of the foot and relieves some of the medial stress.
- If the cyclist has an excessively varus angulation to the knee, spacers can be placed between the pedal and crankarm, widening the pedal stance to align the feet under the knee.
The shoe-cleat-pedal system has evolved over the last few years to include not only clipless fixed-systems which allow adjustment of fore-aft and toe-in/toe-out position, but also floating cleat systems. The floating cleat system allows for varying amounts of foot rotation through the pedaling cycle. Generally, when a cyclist is having knee problems, restriction of five degrees of rotation should be imposed to avoid excessive shear forces to the patellar/extensor system.
Leg length discrepancies may also play a role in overuse disorders in the cyclist. Although not primarily weightbearing, symmetry between sides is still required. Adaptations by the cyclist to a leg length difference may include unequal pelvic rotation and, most commonly, "ankling" (increased dorsiflexion/plantar flexion) while pedaling. This in effect can increase the functional length of the leg, affecting the hip, knee, or ankle adversely.
A general approach to leg length deficiency in the cyclist:1
- Adjust the bicycle first to the long leg.
- Corrections should undercompensate slightly due to the ability to compensated or adapt with increased "ankling."
- If the tibial length discrepancy is 6 mm or more adjust the seat height to allow 25-30 degrees of knee flexion at dead bottom center on the long leg side. Length difference on the short leg can be compensated by using a 4 millimeters or larger lift, or leather shim placed between the shoe and cleat; consider cycling orthotics
- If the femoral length discrepancy is 6 mm or more, adjust seat height to allow 25-30 degrees of knee flexion at dead bottom center on the long leg side.
- Place a 2-3 mm lift or shim on the short leg side between the shoe and the cleat. Move the foot of the short leg back 2 mm on the pedal; move the foot of the long leg forward 2 mm on the pedal. Specific Conditions
Following is a brief discussion of strategies used in the management of some specific conditions.
Chondromalacia or Patellofemoral Arthralgia
The distinction between these two disorders is not always clinically evident. Pathologically, chondromalacia involves degeneration of the back surface of the patella. Patellofemoral arthralgia is "patellar" pain due to irritation of surrounding structures, such as the retinaculum, fat pad, and ligaments, without damage to the hyaline cartilage of the patella. The patient will complain of pain with squatting, going up and down stairs, or with prolonged sitting.
- Evaluate the seat (saddle) position; too low or too far forward of a position will cause increased pressure and pain; correct with a neutral fore-aft seat position and height that allows 25-30 degrees of knee flexion at dead bottom of the pedaling stroke.
- Recommend terminal knee extension exercises and iliotibial band and vastus lateralis stretching.
Patellar Tendinitis
Patellar tendinitis is usually due to eccentric injury. The injury in cycling is often from excessive angular traction during the pedal cycle. The pain is felt with resisted knee extension at any point along the extensor mechanism, including the patella, patellar tendon, or its attachment into the tibial tuberosity.
- Assure correct seat height as described above.
- For an increased valgus angle, use lifts or cants placed between the pedal and shoe on the medial side.
- Restrict floating cleat systems to 5 degrees of rotation
- if there is excessive internal rotation consider cycling orthotics and/or placed the foot in a neutral slightly toed-in position in the cleats.
- Avoid hill work and excessive resistance from big gear riding.
Iliotibial Band (ITB) Syndrome
ITB syndrome is caused by irritation at the lateral epicondyle of the femur. The causative factors include repetitive motion through the arc of 30-40 degrees and/ or a tight, thick, or widened ITB tendon. Pain is felt laterally over the epicondyle with shortening of the ITB evident using the modified Ober's test.
- Check to the cleats for excessive internal rotation position; consider slight external rotation temporarily.
- Check for a seat height that is too high or too far forward.
- Consider the use of spacers on the pedal and crankarm to widen the bicyclist's stance thereby reducing stretch on the ITB.
- If the patient's foot is pronated, consider cycling orthotics.
- If the bicyclist is using fixed cleats, consider switching to floating cleats.
- Stretch the ITB using myofascial release techniques and home/office PNF stretching.
Biceps Femoris Tendinitis
The biceps tendon may be involved when the cyclist complains of posterolateral pain. Tenderness at the insertion into the fibular head or slightly proximal to the attachment are often found.
- Often the seat is too high or too far forward. Consider temporarily decreasing seat height to allow as much as 30-35 degrees of knee flexion at dead bottom center of the pedaling stroke.
- If the bicycle was fit to the long leg side of a cyclist with leg length deficiency, excessive "reaching" for the pedal may cause posterior knee pain due to strain; fit to the long leg, however, correct for the short leg with lifts or shims placed between the pedal and shoe and/or orthotics.
- Evaluate the fibular head for fixation and adjust if found.
With all conditions recommendations in decreasing either intensity or duration of riding should be considered. Additionally, riding on flat terrain and keeping a relatively moderate to fast cadence will compensate to some degree for recommended decreases in resistance.
Reference
1. Holmes JC, Pruitt AL, Whalen NJ. Lower Extremity Overuse in Bicycling. Clin Sports Med. 1994;13:187-203
Thomas Souza, DC, DACBSP
San Jose, California