Muscles/Tendons and Joints

Overuse of tendons and ligaments is one of the major issues when the UE becomes a weight-bearing structure. The sheer and effects of gravity can affect multiple structures. These in turn can affect the bones and joints. These overuse musculoskeletal injuries carry a significant morbidity in this population. Any structure in the UE has the potential of being injured with the new demands of transfers, wheelchair propulsion, and pressure releases. These structures may be only mildly injured, as in tendinitis or strains, or more seriously damaged, as in a tear. Although many of these injuries may be self-limited in able-bodied persons, this is less likely the case, as it is more difficult to rest the injured area in the SCI population and an acute tendinitis can develop into a chronic tendinosis. A list of the muscles and tendons commonly affected is seen in Box 1 .

Nerves

Although we see a significant number of musculoskeletal injuries as mentioned previously, neurologic injuries also play a role in contributing to pain in persons with SCI. These injuries may be difficult to diagnose as a result of their symptoms. Many persons with SCI have residual numbness and tingling, which is a common symptom of early peripheral nerve disease and may, therefore, mask the development of peripheral nerve problems. For instance, persons with C6 or C7 tetraplegia may have hand numbness and tingling at the level of injury, which may mask the early symptoms of either carpal tunnel syndrome or ulnar neuropathy at the elbow. Not only are entrapments possible, but, with the increase in diabetes in the population in general, the SCI population is also at risk for diabetic peripheral neuropathy. Sites and nerves that may be entrapped or injured in the distal upper extremities include the following:

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  Median nerve

  
  
  
  
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    Carpal tunnel syndrome

    
    
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    Pronator syndrome

  
  
  
  
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  Ulnar nerve

  
  
  
  
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    Entrapment at the Guyon canal

    
    
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    Ulnar nerve entrapment at the elbow

  
  
  
  
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  Radial nerve

  
  
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  Other peripheral nerves

Why Use Ultrasound?

One of the issues in the past in assessing pain in SCI is the ability to assess the structure and find the cause of the pain. Although bones may be easily assessed with radiographs, soft tissue injuries require a different modality. Oftentimes, magnetic resonance imaging (MRI) or computerized tomography scans are used. These come with significant costs and need to be scheduled. Over the past decade, with the advent of improved technology, US has started to make the move from the radiology suite to the clinic setting in the form of portable US machines. This modality now allows instant assessment of the structures in question and can help guide treatments. Higher-frequency transducers have allowed for better characterization of tendons and nerves, especially in the more shallow structures as seen in the shoulder, elbow, and wrist. Table 1 illustrates the relative cost and advantages of the major imaging modalities.

Study of the Nerves in the SCI Population

In a study comparing sedentary versus wheelchair racers in SCI, the authors found that the racers had fewer nerve injuries overall compared with sedentary wheelchair users; these subjects were assessed with electrodiagnostic testing and not US and suggested that the overall incidence of injuries was low: 3.2% in racers, and 13.6% in sedentary SCI. This is in contrast to the lifetime incidence mentioned earlier in this article. A more recent article found that asymptomatic median neuropathy may even be as high as 25.5% in the paraplegic population. Still, many other studies have found the prevalence of carpal tunnel syndrome to be between 49% and 73%, and that the prevalence increases with the time elapsed from initial injury.

With this information, researchers have begun to evaluate the median nerve’s reaction to exercise. In one study by Altinok and colleagues, there was an increase in the cross-sectional area (CSA) of the median nerve at the level of the pisiform, but not at the distal radius in those patients with carpal tunnel syndrome (CTS) than in those without, at baseline, before activities. The study also found that differences between the groups were magnified and showed up in other parameters after provocative exercises imitating work-related stresses. Massy-Westropp and colleagues evaluated normal median nerves with exercise and found an increase in CSA after exercise that returned to baseline in 10 minutes. In 2009, Impink and colleagues evaluated the median nerve of paraplegic patients and the response to exercise and found that the nerve responded differently to exercise in those who had symptoms of CTS compared with those who did not have any symptoms. It is therefore likely that these nerves are different at baseline and with short bouts of exercise, but it is not clear what chronic use changes may be seen in this population.

This information may suggest that researchers should start to evaluate the changes in nerves as a result of exercise, not only in those with symptoms, but also to compare those who use manual wheel chairs with able-bodied controls to see if the nerves respond differently over time in a longitudinal study. This might lead to the ability to identify those at risk for future development of nerve injuries after SCI. It also may be important, once the problems are characterized, to develop an intervention that may prevent or reverse the anatomic changes seen on US.

Tendons in the SCI Population

Tendons may change after SCI and the resultant demands placed on them. To understand these changes, it is helpful to understand what adaptations the tendon makes after an SCI. One study in 2006 evaluated tendons below the level of injury in paraplegic patients and able-bodied controls. The findings suggested a decrease in the tendon CSA of the patellar tendon compared with controls. In this study, the tendons of the paraplegic subject underwent electrical stimulation, whereas the able-bodied controls continued their regular recreational activity levels.

There have been several studies attempting to quantitate tendons after exercise. In a study by van Drongelen and colleagues, the biceps tendon CSA and echogenicity were measured before and after a sporting event. They found the echogenicity of the tendon decreased and the size increased. They also found this was directly related to playing time. In one study assessing reliability, they found that the use of one operator was fairly good, but interrater reliability was lacking. They also found that US did not demonstrate changes in tendons, only muscles, after electrical stimulation of lower extremity muscles. Brushoj and colleagues noted that although the CSA may be fairly consistent, the tendon thickness and the thickness measurements were not as reliable.

Another group found the presence of edema in persons with tetraplegia and paraplegia when compared with the able-bodied population. In an attempt to help standardize assessment of tendons in the SCI population, Brose and colleagues developed the US Pathology Rating Scale (USPRS) to quantitate shoulder pathology, and found the changes in the USPRS were related to age, duration of SCI, and weight. Some researchers have advocated a more quantitative set of measures for assessing tendons, but again, the interrater reliability was less than desirable.