In closed injuries, the degree of injury and ischemic tissue may not be apparent and this is a challenge in making soft tissue injury diagnosis and therapeutic decisions [8]. The purpose of this study was to evaluate whether there is a correlation between CK serum levels and fracture pattern as classified by AO classification of fractures. CK serum levels was used as a marker of muscle injury [6,7]. AO classification was used as each pattern of fracture in the classification represents the expected amount of energy involved in the injury [13]. Isolated femur fracture was used following the argument that fractures of the femoral shaft are markers of high-energy injuries and the femur is well enveloped by muscles [10-12].

Normal expected levels of serum CK in general population varies between 35–175 U/L [5]. In this study the laboratory range for CK provided by the laboratory was 35 - 184U/L. Elevated levels clearly represent a strong disruption of striated muscle tissue with concomitant release of intracellular muscle components into the circulation [6,7].

It is well known that there are still marked sex differences in human beings in CK serum levels at rest, with lower values in females than in males [22]. In this study it was also noted that the CK levels even when elevated was still lower in females with similar fracture patterns compared to the male patients. One of the explanations for this could be due to the muscle bulk in females being lower than in males [23]. The second reason could be related to the amount of energy involved during injury; female patients tend to be involved in lower energy accidents compared to the male patients [25]. However, it is notable that the majority of female patients in this study were >50 hence probability of insufficiency fractures was higher which would also explain the low energy fractures hence, low CK serum levels and the fracture pattern sustained [26].

It is well known that the pattern of fracture sustained on the bone is mostly related to the amount of energy involved. Fractures of the femoral shaft are markers of high-energy injuries and since the femur is well enveloped by muscles; some of the energy is absorbed by the soft tissue envelope [10-12]. However, in this study the levels of CK did not match very well with the fracture pattern but there was a definite correlation between the CK levels and amount of energy involved during injury. Patients who sustained fractures through high energy mechanism or direct force/crush injury type to the thigh/femur had higher levels of CK regardless of the fracture pattern sustained (Figure 3). The authors thought this could be explained by assuming that in those fractures of lower grading as per AO that had higher levels of CK than expected, the reason could be because most of the force involved was absorbed by the muscle envelope therefore, less of the energy reached the bone to cause a higher-grade fracture pattern.  As already defined earlier, a fracture, is a soft tissue injury with a break in the bone [13]. The other reasons could be of soft tissue injury such as direct impact, implosion, and displacement during transportation, degree of fracture displacement, inflammatory process, and ischemia due to blood supply interruption or edema. These reasons which the investigator did not have control of could explain the reason for the mismatch between CK levels and fracture pattern. It is important to note that none of the patients had signs of compartment syndrome clinically or vascular injury as checked by measuring the ABI. The other factor to consider that may explain the mismatch was the fact that all these patients received intravenous fluids as part of their initial resuscitation measures. The effect of intravenous fluid on the levels of CK could have been through dilution or increased clearance through the kidneys [27]. Also, to be considered is whether all the CK released from the injured muscles actually leaked into circulation.

Patients who sustained pathological fractures had CK levels within normal range. The mechanism of injury in these patients was indirect rotational forces which seemed to be transmitted through bone and muscle but was not sufficient to cause significant muscle injury and only caused a break in the bone at an area of weakness [28].