Stress fractures make up about 10% of all sport-related injuries, and the most common site is the tibia, a classic overuse injury among runners. Tibial stress fractures (TSF) typically require six to eight weeks for recovery. Women are reported to be at significantly greater risk than men. Several structural and mechanical factors have been shown to contribute to the onset of stress fractures. Bone structure is a key one, with research showing that individuals who go on to develop TSF have reduced tibial bone width and ‘area moment of inertia’. (Quick lesson in biomechanics: the area moment of inertia measures the bone’s ability to resist bending, so the larger the moment of inertia the less the bone will bend.) In addition, tibial cross-sectional area, a strong determinant of area moment of inertia, is smaller in male runners with a history of stress fracture.
Anatomical alignment has also been identified as a potential key contributor to lower-leg stress fracture. Research has shown that athletes with such stress fractures often have varus malalignment (inward angulation of the bone of joint, such as in a knock-kneed person, where the femur is deviated inward in relation to the hip) of knee, shin, heel or forefoot. During compressive loading, varus malalignment is likely to result in greater bending pressure on the tibia.
The quantity or ‘dose’ of loading, increased ground reaction forces, loading rates and peak braking forces may also all contribute to the onset of stress fractures.
Researchers in the US recently conducted a cross-sectional study to establish whether differences in structure (eg varus, tibial area moment of inertia) and running mechanics exist between trained female distance runners with a history of TSF and those who have never sustained a fracture (‘Biomechanical factors associated with tibial stress fracture in female runners’, Medicine and Science in Sports and Exercise2006; 38 (2):323-328).
The team hypothesised that runners who had previously had a TSF would experience problems in the following areas:
* Increased vertical loading rates
* Increased vertical impact peak
* Increased loading rates during braking
* Increased knee and ankle joint torsional stiffness in the sagittal plane
* Increased tibial acceleration
* Decreased knee flexion movement.
* Increased tibial varum (inwards deviation) during standing
* Decreased tibial area moment of inertia.
Female runners aged 18-45 with a rear foot strike technique, running at least 32km a week, took part in the study. They were divided into two groups: 20 subjects with a history of TSF and 20 with no previous lower extremity bony injuries. Kinematic and kinetic data were collected while the participants ran at 13.32kph. Structural measurements were completed using a combination of X-ray studies of both tibiae in standing to assess tibial area moment of inertia and tibial cross-section; plus measurements of the extent of tibial varum.
The results indicated that a history of TSF in female runners is associated with increases in several dynamic loading-related variables. The TSF group had significantly greater vertical loading rates and peak tibial shock when compared to the control group. A trend was also noted toward greater knee stiffness and impact peak in the TSF group. Loading rates during braking, however, were not different between the groups. No significant differences were found in the structural measures of the tibial area moment of inertia and varum angle.
Femoral fracture protocol
Stress fractures of the femoral shaft are rare, found mainly in long- and middle-distance runners, military recruits and, according to some research, more among women than men. They are also difficult to diagnose and, if not treated correctly, have high rates of complications. These stress fractures usually occur in the upper third of the femur. The junction of the upper and middle thirds of the femur is particularly susceptible to repeated submaximal stress. Researchers from Croatia have recently developed a four- stage step-by-step procedure that will allow clinicians to treat this type of injury in a structured manner (‘Stress fractures of the femoral shaft in athletes: a new treatment algorithm’, British journal of Sports medicine 2006; 40:518-520).
Seven high level athletes – long- and middle-distance runners aged 17 to 21 – who had been diagnosed with stress fractures of the femoral shaft, were treated in the department of orthopaedic surgery at the University of Zagreb during a nine-year period. The athlete’s histories indicated that all had vague anterior thigh pain, especially during and after training sessions.
The proposed algorithm was used on each of the athletes over four phases. Each phase lasted three weeks, and the move to the next phase was based on the result of two tests carried out at the end of the previous phase:
Fulcrum test– the athlete sits on an examination table with lower legs dangling. The clinician places their arm under the patient’s thigh, acting as a fulcrum while with the other hand the clinician presses down on the knee. This action is repeated several times with the clinician moving the fulcrum further up the femur each time. At the point under the stress fracture, gentle pressure on the knee produces increased discomfort.
Hop test– the patient attempts to hop on the injured leg, reproducing pain if an undisplaced stress fracture is present. If these two tests were positive after three weeks, the patient returned to the beginning of that phase.
The four phases of the protocol are:
Phase 1 (symptomatic)– patient walks with the aid of crutches and is instructed not to weight-bear on affected leg.
Phase 2 (asymptomatic)– the patient walks normally. Non-impact training (eg aqua running, swimming, cycling), and strength development (only upper body and unaffected leg) are introduced.
Phase 3 (Basic)– training is permitted for upper and lower body strength development; straight-line running every 2nd day with gradual increases in distance, and cycling (stationary bike).
Phase 4 (resuming)– the athlete returns to normal training under the guidance of their coach.
All of the athletes in the study returned to full training 12-18 weeks after the start of the treatment. The research team noted the importance of early diagnosis. The athletes with the longest recovery time had also experienced the longest delay in diagnosis (4-8 weeks compared to 1-2 weeks). During the follow-up period (48-96 months), there was no recurrence of discomfort or pain, and all the athletes successfully returned to competition. The team concluded that the algorithm is an optimal treatment protocol for femoral shaft stress fractures in athletes, avoiding common complications and difficulties.