<!-- STEPPING OUT --> <span style="color: #000000;">The knee is the largest and strongest joint in the body, consisting of the distal femur, the proximal end of the tibia, and the patella. The ends of these three bones are covered with cartilage that protects and cushions them as the knee bends and straightens. There are two wedge-shaped pieces of fibrocartilage—the lateral meniscus and the medial meniscus—that act as shock absorbers between the femur and tibia. They are tough and rubbery to help cushion and stabilize the joint, and are surrounded by a synovial membrane that lubricates the cartilage and reduces friction. There are also the cruciate and collateral ligaments, and the joint is crossed by several tendons.</span> <span style="color: #000000;">Although exact numbers are difficult to determine, mechanical knee pain accounts for a significant portion of exercise- and running-related injuries. Knee pain is a complex subject and leading researchers advance more than one theory of etiology. This article provides an overview of the topic and presents some treatment options that can be used as a starting point for further investigation.</span> <div style="width: 575px; margin: 5px auto 10px auto;"><span style="color: #000000;"><img src="https://opedge.com/Content/OldArticles/images/2016-11/2016-11_06-01.jpg" alt="diagram of knee with legend" /></span></div> <h3 style="color: #cd1628;"><span style="color: #000000;">Biomechanics</span></h3> <span style="color: #000000;">It has been proposed that mechanically induced knee pain has its origin in the biomechanics of the lower limb. In normal gait, heel strike occurs with the foot in an inverted position. As loading response proceeds, the plantar foot everts rapidly. The resulting pronation of the subtalar joint (STJ) initiates an eversion of the calcaneus and a lowering of the medial longitudinal arch. This, in turn, allows internal rotation of the tibia. Above the tibia, the femur also rotates and there is a transverse plane internal rotation of the knee. If pronation is excessive, lower-limb compensations include knee abduction or hip adduction. The harmonic sequence of STJ pronation (frontal plane) correlating to internal tibial rotation (transverse plane) is necessary for shock absorption, but it can affect the knee, increasing patellofemoral (PF) joint contact and creating stress locally.</span> <span style="color: #000000;">It is thought, though not universally accepted, that the torque from knee rotation and abduction may be the cause of pain. When a patient demonstrates foot pronation late in the gait cycle, failing to resupinate appropriately, the resulting knee valgus strains the tendons and ligaments, potentially altering patella alignment. Foot orthotics and physical therapy can address some of these characteristics by properly supporting the foot, adjusting the timing and duration of pronation, and strengthening the muscle groups involved. Not all patients will respond to these interventions but it is possible to quickly test their potential benefit. You can often determine if the pain is mechanical in origin by using some combination of in-office prefabricated foot orthotics, taping, or sole wedges.</span> <span style="color: #000000;">There is good evidence supporting the use of custom foot orthotics, and three papers highlighting their efficacy were cited in an article in the September 2016 issue of <em>The O&P EDGE</em> (<a style="color: #000000;" href="https://opedge.dev/4074">www.oandp.com/articles/2016-09_08.asp</a>). When designing foot orthotics for knee pain, the device should fully support the medial column of the foot, helping reduce pronation and knee valgus, thereby limiting the force moments at the knee. Usually a full-width, semirigid, thermoplastic orthotic works best. A deep heel cup and a zero degree, flat extrinsic post provides good stability, which restricts calcaneal eversion and avoids end range of motion (ROM). Interestingly, the provision of foot orthotics does not necessarily translate to visibly better biomechanics at the knee. Some studies have noted the benefit of foot orthotics without observing measurable changes in kinematics. It seems part of their effect may be in altering the loading rate and timing of forces along the closed kinetic chain rather than simply aligning the leg and reducing knee valgus.</span> [caption id="" align="alignright" width="315"]<img class="" style="margin: 4px; border: 1px solid #000000;" src="https://opedge.com/Content/OldArticles/images/2016-11/2016-11_06-02.jpg" alt="" width="315" height="450" /> Ground reaction force and gravity induce pronation during the loading response phase of gait. The combined effect of lowering the medial longitudinal arch (MLA) and subsequent internal rotation of the tibia can lead to knee valgus.[/caption] <h3 style="color: #cd1628;"><span style="color: #000000;">Research</span></h3> <span style="color: #000000;">Intuitively, the notion of lower-limb rotation and knee abduction provides a framework to consider the cause of knee pain. However, numerous studies examining knee kinetics and kinematics indicate there are other subtle factors that weigh into the equation. For example, not all people with flat feet experience knee pain, and simply raising the medial arch does not predictably eliminate the problem. In recent years, an academic forum has been organized to gather and discuss the best available research. They have met biennially since 2009 to develop consensus statements on terminology, etiology, and treatments. For a more in-depth look at their work and a host of further references, search "International Patellofemoral Pain Research Retreat" on PubMed at <a style="color: #000000;" href="https://opedge.dev/1477">www.ncbi.nlm.nih.gov/pubmed</a>.</span> <span style="color: #000000;">One emerging idea is there may be subgroups within patient cohorts who respond differently to treatments. For example, women are far more likely to experience PFPS than men, and teenage girls are at more than twice the risk compared to boys. This suggests the causes may be different for men and women and that perhaps the treatment plans should also be different. At the proximal end of the leg, other researchers have noted a link between hip mechanics and PFPS. In some studies, hip strength and ROM (abduction and extension) have been correlated to PFPS. The underlying cause of knee pain is an area rich in opportunity for investigation, and much work needs to be done to develop a comprehensive theory and patient-specific treatment protocols.</span> <h2 style="color: #000000; text-align: left;"><span style="color: #000000;">THE NAME GAME</span></h2> <span style="color: #000000;"><strong>OSGOOD-SCHLATTER DISEASE</strong> is a common cause of knee </span><span style="color: #000000;">pain in growing adolescents. It is an inflammation of the </span><span style="color: #000000;">area just below the knee where the patella tendon attaches to </span><span style="color: #000000;">the tibia. Osgood-Schlatter disease most often occurs during </span><span style="color: #000000;">growth spurts. Children who participate in athletics—</span><span style="color: #000000;">especially running and jumping sports—are at an increased </span><span style="color: #000000;">risk and may experience pain, tenderness, or swelling at the </span><span style="color: #000000;">tibial tubercule.</span> <span style="color: #000000;"><strong>SINDING-LARSEN-JOHANSSON DISEASE</strong> is another cause of </span><span style="color: #000000;">anterior knee pain, again usually seen in adolescents around </span><span style="color: #000000;">the time of a growth spurt. It presents as activity-related </span><span style="color: #000000;">anterior knee pain and there is typically tenderness over the </span><span style="color: #000000;">inferior pole of the patella. The mechanism is thought to be </span><span style="color: #000000;">persistent, repetitive traction by the patella tendon, possibly </span><span style="color: #000000;">due to tight quadriceps muscles or a sudden relative lengthening </span><span style="color: #000000;">of the femur. It may be considered similar to Osgood-</span><span style="color: #000000;">Schlatter disease except it occurs more superior, at the distal </span><span style="color: #000000;">end of the patella instead of at the tibial tubercule. For both </span><span style="color: #000000;">conditions, therapies of rest, stretching and strengthening, </span><span style="color: #000000;">and sometimes the use of anti-inflammatory medications, </span><span style="color: #000000;">can prove beneficial. Foot orthotics help in certain cases, </span><span style="color: #000000;">especially if excessive foot pronation is thought to be contributing </span><span style="color: #000000;">torsional force at the knee.</span> <span style="color: #000000;"><strong>CHONDROMALACIA PATELLA</strong>, sometimes referred to as runner's </span><span style="color: #000000;">knee, is an inflammation or chronic irritation of the </span><span style="color: #000000;">posterior surface of the patella. The distinguishing characteristic </span><span style="color: #000000;">of chondromalacia is softening of the cartilage, and </span><span style="color: #000000;">patients sometimes also report a grinding sensation. The </span><span style="color: #000000;">patella cartilage acts as a natural shock absorber, and once </span><span style="color: #000000;">erosion occurs and the surface is no longer smooth, movement </span><span style="color: #000000;">can become painful. It may occur due to an acute </span><span style="color: #000000;">injury or overuse from participating in high-activity sports. </span><span style="color: #000000;">Pain often feels worse after prolonged sitting. Rest may </span><span style="color: #000000;">help. But if the root cause is patella malalignment or muscle </span><span style="color: #000000;">imbalance, it may be necessary to seek physical therapy or </span><span style="color: #000000;">arthroscopic surgery.</span> <span style="color: #000000;"><strong>PATELLOFEMORAL PAIN SYNDROME (PFPS)</strong> is defined as </span><span style="color: #000000;">diffuse pain around or behind the patella, which is aggravated </span><span style="color: #000000;">by activities that load the PF joint, such as squatting, running, </span><span style="color: #000000;">jumping, and ascending and descending stairs. The </span><span style="color: #000000;">term is used rather broadly but should be kept distinct </span><span style="color: #000000;">from tendinopathies and ligament insufficiencies. It differs </span><span style="color: #000000;">from chondromalacia in that there is no cartilage damage. </span><span style="color: #000000;">Symptoms include crepitus, tenderness on palpation of the </span><span style="color: #000000;">patella edges, and pain upon straightening the knee following </span><span style="color: #000000;">sitting. Currently, the best available test is to check for </span><span style="color: #000000;">anterior knee pain elicited during a squat.</span> <span style="color: #000000;"><strong>PES ANSERINE BURSITIS</strong> is medial knee pain resulting from </span><span style="color: #000000;">inflammation of the bursa located between the tibia and three </span><span style="color: #000000;">tendons of the hamstring muscles. Pain usually increases </span><span style="color: #000000;">with exercise and is felt about two to three inches below the </span><span style="color: #000000;">medial knee. It can be the result of overuse, sudden exertion, </span><span style="color: #000000;">tight hamstrings, obesity, or other factors that put stress on </span><span style="color: #000000;">the knee. As with any bursitis, conservative measures, such as </span><span style="color: #000000;">rest and icing, often help. In addition, foot orthotics that limit </span><span style="color: #000000;">pronation have been shown as beneficial.</span> <span style="color: #000000;"><strong>KNEE OSTEOARTHRITIS</strong> is a distinct degenerative joint disease </span><span style="color: #000000;">characterized by stiffness and pain and should be considered </span><span style="color: #000000;">separate from anterior knee pain. Likewise, any </span><span style="color: #000000;">structural knee damage or ligamentous injuries should be </span><span style="color: #000000;">differentiated from those that are mechanical in origin.</span> <span style="color: #000000;"><em>Séamus Kennedy, BEng (Mech), CPed, is president and co-owner of Hersco Ortho Labs, New York. He can be contacted by visiting <a style="color: #000000;" href="https://opedge.dev/2966">www.hersco.com</a>.</em></span>
