Sports Medicine 14 (3): 149-156, 1992 0112-1642/92/0009-0149/$04.00/0 © Adis International Limited. All rights reserved. SPOl162
Lower Extremity Injury
Biomechanical Factors Associated with Chronic Injury to the Lower Extremity David A. Winter and Patrick J. Bishop
Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
The lower extremity of the body is involved in virtually all athletic movements (except certain phases of upper extremity gymnastic movements) and in the many sub-tasks associated with the major goal of specific athletic events. These sub-tasks can be generalised as follows: shock (energy) absorption and control of vertical collapse during any weight acceptance phase; balance and posture control of the upper part of the body; energy generation associated with forward and upward propulsion; and control of direction changes of the centre of mass of the body. A muscle or muscle group can be simultaneously involved in more than one of these sub-tasks. During level running, for example, the hip extensor muscles serve not only to control the dynamic balance of the upper body head and torso (Ruder 1989; Winter 1987) but also to assist the knee extensors to absorb energy and prevent knee collapse (Winter 1984). Given the instantaneous and repetitive demands put on all supporting tissue it is not surprising that injury to the lower extremity is not uncommon. It is impossible to understand these injuries without a detailed biomechanical analysis of athletic movement. Unfortunately, there are few biomechanical analyses of the forces that are responsible for the injuries. Often discussion is based on kinematic variables or, at best, with ground reaction forces under the support foot. Injuries fall into 2 causal categories. Firstly, there are single event injuries resulting from a well recognised traumatic incident: a football tackle or a
twisted ankle resulting from landing on uneven ground. In such events the cause/effect relationship is usually fairly obvious. However, chronic injuries are somewhat difficult to analyse because all the forces involved are below the single event injury threshold, and also the repetitive damaging forces must be analysed over the total period of the movement. One way to narrow our search is to first examine the injury statistics and the nature and exact location of each chronic injury. With this retrospective information we can hopefully focus our biomechanical analyses on specific tissues and see when, during the movement cycle, the tissue undergoes maximum stress.
1. Chronic Injuries: Statistics and Location Several studies have been undertaken to examine the nature, cause and severity of injuries to runners. Many of these have been primarily concerned with the underlying aetiology of running injuries (Jacobs & Berson 1986; Macera et al. 1989; Powell et al. 1986; Walter et al. 1988, 1989) while others have been concerned with detailing the types of injury most often associated with running. One of the earliest attempts to quantify lower extremity injury comes from James et al. (1978) who evaluated 180 runners with 232 conditions. 71% of the complaints fell into 6 categories, namely knee pain (29%), posterior tibial syndrome (13%),
150
Achilles tendinitis (11%), plantar fasciitis (7%), stress fractures (6%) and iliotibial tract tendinitis (5%). The most common knee problem was chondromalacia (25%) but a significant amount of peripatellar pain (15%) was also noted. Clement et al. (1981) reported similar findings in their retrospective study of 1650 patients with 1819 injuries. In a study by Marti et al. (1988) of 4358 men entered in the 16km Bern Grand-Prix road race of 1984, 46% had sustained jogging injuries during the previous year. Injury locations were defined for all grade III injuries (i.e. those that produced 'involuntary complete interruption of running of at least 2 weeks' duration'). Of the 877 injuries reported the most common locations were the knee (28%), tibial region including Achilles tendon (30%) and the foot and ankle (29%). Similar types of injury were identified by Lysholm & Wiklander (1987) in a group of 39 runners belonging to 2 track clubs in Sweden. One of the difficulties in interpreting the data from these studies is with the terminology used to describe the various injuries. For the purpose of this review the major injuries associated with running are defined as follows. Patellofemoral pain syndrome is a condition used to describe generalised anterior knee pain, often equated with the term chondromalacia which is a softening or degeneration of the articular cartilage on the posterior surface of the patella. For chondromalacia to be present, it must be accompanied by retropatellar crepitation and a definite facet tenderness (James et al. 1978). Patellofemoral pain syndrome is often associated with faulty tracking of the patella in the patellar groove due to either malalignment, muscle imbalance or both (Brody 1980). Biomechanically, the condition is exacerbated in running by the compressive component of the quadriceps muscle force which forces the patella against the groove and by the lateral shearing component of the quadriceps muscle force as the patella moves relative to the femur during execution of the knee's range of motion. Posterior tibial syndrome, or tibial stress syndrome (Clement et aI. 1981) or medial tibial stress syndrome (Mubarak et al. 1982), is a condition
Sports Medicine 14 (3) 1992
characterised by pain and tenderness along the posterior medial aspect of the tibia over the posterior tibialis muscle and tendon. Such pain is often referred to as 'shin splints' but that term is nonspecific and has come to be associated with almost all types of leg pain (James et al. 1978). Tibial stress syndrome usually begins as a tendinitis but progresses to a periostitis. The condition is believed to be associated with midstance in running where the foot pro nates and the tibia rotates internally pulling the posterior tibialis tendon and muscle at its attachment to both the tibia and the interosseous membrane (Brody 1980). Michael and Holder (1985), however, have implicated the soleus rather than the tibialis posterior as the muscle involved in medial tibial stress syndrome. Their anatomical study demonstrated that the tibialis posterior originates a considerable distance from the medial border of the posterior tibia (pain site) and that the muscle belly is higher in location than the usual site of pain. Conversely, the soleus has a tough aponeurotic covering, which extends directly to the posterior medial border of the tibia, for three-fourths of its length where it attaches at its origin. The insertion is complex but its tendinous portion inserts on the medial onethird of the calcaneus. Biomechanically, this insertion makes the soleus vulnerable to excessive elongation when the heel is pronated (Michael & Holder 1985) and this action may be responsible for the complaint of tibial leg pain in runners. Achilles tendinitis is a common disorder in runners, characterised by pain and inflammation in the Achilles tendon. This tendonopathy is believed to be aggravated by running uphill, by hard landing when running downhill and by wearing shoes with rigid soles. In those with heel or forefoot varus or rear foot valgus, excessive stress is placed on the Achilles tendon as the foot is pronated upon moving into midstance (Brody 1980; Clement et al. 1984). During foot pronation in running, the Achilles tendon will be drawn medially because of the internal rotation of the tibia which accompanies pronation. The tendon will be drawn laterally during foot supination and foot takeoff as the tibia rotates externally. Both pronation and supination
Lower Extremity Injury
are accompanied by flexion and extension of the knee, respectively, during running. In those who overpronate, the foot may still be pronated after knee extension has begun and the external tibial rotation generated by knee extension will conflict with the exaggerated internal rotation produced by prolonged pronation. These conflicting rotary forces may be responsible for 'wringing out' the vascular vessels in the Achilles tendon and peritendon, causing vascular impairment and subsequent degenerative changes (Clement et al. 1984) which become manifest as irritation and pain. Further support for vascular changes to these areas can be found in Kvist et al. (1988). Plantar fasciitis is a common source of heel pain in runners. It is considered to be a strain or tearing of the long plantar aponeurosis accompanied by an exquisite pain at the attachment site on the calcaneus (Taunton et al. 1982). In those with heel or forefoot varus or with rear foot valgus, which produces a functional pes planus and excessive pronation when running, excessive traction is placed on the medial plantar fascia and an inflammatory reaction at the calcaneal attachment develops. Stress fractures are common injuries and may constitute between 4.7% and 15.6% of injuries to runners (Matheson et al. 1987). In 1 study of 320 cases the tibia was the most frequent site of injury (49%), running was the most frequent cause (69%), and there was a strong association between tibial stress fractures and pronated feet (Matheson et al. 1987). Biomechanically, excessive pronation is believed to cause an increase in tibial torsion during the support phase of running, leading to stress fractures which are commonly located in the distal third of the tibia. Iliotibial band syndrome - a condition also referred to as iliotibial band friction syndrome - is an overuse injury found in long-distance runners produced by repeated flexion/extension of the knee (Brody 1980; Noble 1980). It is characterised by pain on the lateral aspect of the knee in close relation to the lateral femoral epicondyle (Noble 1980). As the band passes over this region on its way to its attachment on the lateral tibial condyle (Gerdy's tubercle) it is pulled anteriorly in flexion
151
by the tensor fascia lata and posteriorly in extension by the gluteus maximus (Sutker et al. 1981). The condition usually occurs in runners with a knee alignment of neutral or varus (Sutker et al. 1981) or with tibia vara and a pes planus (Brody 1980).
2. Biomechanics Research
2.1 Ground Reaction Forces and Pressure Distribution The vast majority of the biomechanics research associated with running has revolved about the footwear, the running surface and the reaction forces and pressure patterns under the footwear. Review articles and symposia (Nigg & Kerr 1983; Robbins & Gouw 1990) and books (Cavanagh 1983; Nigg 1986) have been written on the subject. Rather than re-review the many references contained within these reports it is sufficient to summarise the findings relating to the kinematics of the foot and to the ground reaction forces and pressures and how they change with footwear and running surface. Also, it is the intention of the authors to relate these findings in a cause/effect relationship to the chronic running injuries and their sites. The vertical ground reaction force pattern is characterised by a short duration initial spike followed by a broader wave that peaks in midstance. The first peak is referred to as passive, the latter as the active phase. Simultaneous recordings of vertical ground reaction forces and acceleration of the lower limb skeletal system have shown a correlation during the initial impact phase (Nigg 1986). An accelerometer located on the lateral malleolus recorded a spike of acceleration in phase with the spike and rate of buildup of force increases with the speed of running. The peak amplitude is attenuated during shod versus barefoot running and also with a change from hard to s
Lower Extremity Injury
Biomechanical Factors Associated with Chronic Injury to the Lower Extremity David A. Winter and Patrick J. Bishop
Department of Kinesiology, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
The lower extremity of the body is involved in virtually all athletic movements (except certain phases of upper extremity gymnastic movements) and in the many sub-tasks associated with the major goal of specific athletic events. These sub-tasks can be generalised as follows: shock (energy) absorption and control of vertical collapse during any weight acceptance phase; balance and posture control of the upper part of the body; energy generation associated with forward and upward propulsion; and control of direction changes of the centre of mass of the body. A muscle or muscle group can be simultaneously involved in more than one of these sub-tasks. During level running, for example, the hip extensor muscles serve not only to control the dynamic balance of the upper body head and torso (Ruder 1989; Winter 1987) but also to assist the knee extensors to absorb energy and prevent knee collapse (Winter 1984). Given the instantaneous and repetitive demands put on all supporting tissue it is not surprising that injury to the lower extremity is not uncommon. It is impossible to understand these injuries without a detailed biomechanical analysis of athletic movement. Unfortunately, there are few biomechanical analyses of the forces that are responsible for the injuries. Often discussion is based on kinematic variables or, at best, with ground reaction forces under the support foot. Injuries fall into 2 causal categories. Firstly, there are single event injuries resulting from a well recognised traumatic incident: a football tackle or a
twisted ankle resulting from landing on uneven ground. In such events the cause/effect relationship is usually fairly obvious. However, chronic injuries are somewhat difficult to analyse because all the forces involved are below the single event injury threshold, and also the repetitive damaging forces must be analysed over the total period of the movement. One way to narrow our search is to first examine the injury statistics and the nature and exact location of each chronic injury. With this retrospective information we can hopefully focus our biomechanical analyses on specific tissues and see when, during the movement cycle, the tissue undergoes maximum stress.
1. Chronic Injuries: Statistics and Location Several studies have been undertaken to examine the nature, cause and severity of injuries to runners. Many of these have been primarily concerned with the underlying aetiology of running injuries (Jacobs & Berson 1986; Macera et al. 1989; Powell et al. 1986; Walter et al. 1988, 1989) while others have been concerned with detailing the types of injury most often associated with running. One of the earliest attempts to quantify lower extremity injury comes from James et al. (1978) who evaluated 180 runners with 232 conditions. 71% of the complaints fell into 6 categories, namely knee pain (29%), posterior tibial syndrome (13%),
150
Achilles tendinitis (11%), plantar fasciitis (7%), stress fractures (6%) and iliotibial tract tendinitis (5%). The most common knee problem was chondromalacia (25%) but a significant amount of peripatellar pain (15%) was also noted. Clement et al. (1981) reported similar findings in their retrospective study of 1650 patients with 1819 injuries. In a study by Marti et al. (1988) of 4358 men entered in the 16km Bern Grand-Prix road race of 1984, 46% had sustained jogging injuries during the previous year. Injury locations were defined for all grade III injuries (i.e. those that produced 'involuntary complete interruption of running of at least 2 weeks' duration'). Of the 877 injuries reported the most common locations were the knee (28%), tibial region including Achilles tendon (30%) and the foot and ankle (29%). Similar types of injury were identified by Lysholm & Wiklander (1987) in a group of 39 runners belonging to 2 track clubs in Sweden. One of the difficulties in interpreting the data from these studies is with the terminology used to describe the various injuries. For the purpose of this review the major injuries associated with running are defined as follows. Patellofemoral pain syndrome is a condition used to describe generalised anterior knee pain, often equated with the term chondromalacia which is a softening or degeneration of the articular cartilage on the posterior surface of the patella. For chondromalacia to be present, it must be accompanied by retropatellar crepitation and a definite facet tenderness (James et al. 1978). Patellofemoral pain syndrome is often associated with faulty tracking of the patella in the patellar groove due to either malalignment, muscle imbalance or both (Brody 1980). Biomechanically, the condition is exacerbated in running by the compressive component of the quadriceps muscle force which forces the patella against the groove and by the lateral shearing component of the quadriceps muscle force as the patella moves relative to the femur during execution of the knee's range of motion. Posterior tibial syndrome, or tibial stress syndrome (Clement et aI. 1981) or medial tibial stress syndrome (Mubarak et al. 1982), is a condition
Sports Medicine 14 (3) 1992
characterised by pain and tenderness along the posterior medial aspect of the tibia over the posterior tibialis muscle and tendon. Such pain is often referred to as 'shin splints' but that term is nonspecific and has come to be associated with almost all types of leg pain (James et al. 1978). Tibial stress syndrome usually begins as a tendinitis but progresses to a periostitis. The condition is believed to be associated with midstance in running where the foot pro nates and the tibia rotates internally pulling the posterior tibialis tendon and muscle at its attachment to both the tibia and the interosseous membrane (Brody 1980). Michael and Holder (1985), however, have implicated the soleus rather than the tibialis posterior as the muscle involved in medial tibial stress syndrome. Their anatomical study demonstrated that the tibialis posterior originates a considerable distance from the medial border of the posterior tibia (pain site) and that the muscle belly is higher in location than the usual site of pain. Conversely, the soleus has a tough aponeurotic covering, which extends directly to the posterior medial border of the tibia, for three-fourths of its length where it attaches at its origin. The insertion is complex but its tendinous portion inserts on the medial onethird of the calcaneus. Biomechanically, this insertion makes the soleus vulnerable to excessive elongation when the heel is pronated (Michael & Holder 1985) and this action may be responsible for the complaint of tibial leg pain in runners. Achilles tendinitis is a common disorder in runners, characterised by pain and inflammation in the Achilles tendon. This tendonopathy is believed to be aggravated by running uphill, by hard landing when running downhill and by wearing shoes with rigid soles. In those with heel or forefoot varus or rear foot valgus, excessive stress is placed on the Achilles tendon as the foot is pronated upon moving into midstance (Brody 1980; Clement et al. 1984). During foot pronation in running, the Achilles tendon will be drawn medially because of the internal rotation of the tibia which accompanies pronation. The tendon will be drawn laterally during foot supination and foot takeoff as the tibia rotates externally. Both pronation and supination
Lower Extremity Injury
are accompanied by flexion and extension of the knee, respectively, during running. In those who overpronate, the foot may still be pronated after knee extension has begun and the external tibial rotation generated by knee extension will conflict with the exaggerated internal rotation produced by prolonged pronation. These conflicting rotary forces may be responsible for 'wringing out' the vascular vessels in the Achilles tendon and peritendon, causing vascular impairment and subsequent degenerative changes (Clement et al. 1984) which become manifest as irritation and pain. Further support for vascular changes to these areas can be found in Kvist et al. (1988). Plantar fasciitis is a common source of heel pain in runners. It is considered to be a strain or tearing of the long plantar aponeurosis accompanied by an exquisite pain at the attachment site on the calcaneus (Taunton et al. 1982). In those with heel or forefoot varus or with rear foot valgus, which produces a functional pes planus and excessive pronation when running, excessive traction is placed on the medial plantar fascia and an inflammatory reaction at the calcaneal attachment develops. Stress fractures are common injuries and may constitute between 4.7% and 15.6% of injuries to runners (Matheson et al. 1987). In 1 study of 320 cases the tibia was the most frequent site of injury (49%), running was the most frequent cause (69%), and there was a strong association between tibial stress fractures and pronated feet (Matheson et al. 1987). Biomechanically, excessive pronation is believed to cause an increase in tibial torsion during the support phase of running, leading to stress fractures which are commonly located in the distal third of the tibia. Iliotibial band syndrome - a condition also referred to as iliotibial band friction syndrome - is an overuse injury found in long-distance runners produced by repeated flexion/extension of the knee (Brody 1980; Noble 1980). It is characterised by pain on the lateral aspect of the knee in close relation to the lateral femoral epicondyle (Noble 1980). As the band passes over this region on its way to its attachment on the lateral tibial condyle (Gerdy's tubercle) it is pulled anteriorly in flexion
151
by the tensor fascia lata and posteriorly in extension by the gluteus maximus (Sutker et al. 1981). The condition usually occurs in runners with a knee alignment of neutral or varus (Sutker et al. 1981) or with tibia vara and a pes planus (Brody 1980).
2. Biomechanics Research
2.1 Ground Reaction Forces and Pressure Distribution The vast majority of the biomechanics research associated with running has revolved about the footwear, the running surface and the reaction forces and pressure patterns under the footwear. Review articles and symposia (Nigg & Kerr 1983; Robbins & Gouw 1990) and books (Cavanagh 1983; Nigg 1986) have been written on the subject. Rather than re-review the many references contained within these reports it is sufficient to summarise the findings relating to the kinematics of the foot and to the ground reaction forces and pressures and how they change with footwear and running surface. Also, it is the intention of the authors to relate these findings in a cause/effect relationship to the chronic running injuries and their sites. The vertical ground reaction force pattern is characterised by a short duration initial spike followed by a broader wave that peaks in midstance. The first peak is referred to as passive, the latter as the active phase. Simultaneous recordings of vertical ground reaction forces and acceleration of the lower limb skeletal system have shown a correlation during the initial impact phase (Nigg 1986). An accelerometer located on the lateral malleolus recorded a spike of acceleration in phase with the spike and rate of buildup of force increases with the speed of running. The peak amplitude is attenuated during shod versus barefoot running and also with a change from hard to s
