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An Evaluation of a Clinical Method to Assess Malunion of Little Finger Metacarpal FracturesFrom the Departments of Trauma and Orthopaedic Surgery, Queen’s Medical Centre, University Hospital, Nottingham, UK Correspondence: Prof. T. R. C. Davis, Department of Trauma and Orthopaedic Surgery, Queen’s Medical Centre, University Hospital, Nottingham NG7 2UH, United Kingdom Tel.: +44 1159249924 x 44337; Fax: +44 1159209921. E-mail:tim.davis{at}nuh.nhs.uk
This study assessed the reliability, responsiveness and validity of two clinical measurements for the assessment of malunion of little finger metacarpal neck and shaft fractures. Both compared the relative lengths of the ring and little fingers in the injured and contralateral hands. One measurement was taken with the metacarpophalangeal joints extended (straight-MCP), and the other with them flexed to 90° (90-MCP). Ninety-five percent of the differences between the relative lengths of the ring and little fingers in the two hands of 50 normal subjects were less than 3 mm and the 95% limits of agreement for repeat measurements (intra-observer reproducibility) was ±1 mm for both measurements. Both measurements were significantly altered in a group of 218 patients with a past history of a metacarpal shaft or neck fracture. Although both measurements correlated with the patient’s assessment of the cosmetic result (p = 0.01), neither measurement correlated with the severity of palmar angulation of the fracture at presentation. It is concluded that these measurements are reliable and responsive, but their validity is uncertain.
Key Words: metacarpal fractures • shortening • malunion
Metacarpal neck and shaft fractures frequently unite with palmar angular deformity or shortening. Such malunion is usually assessed with plain X-rays, which is practical when assessing patients with troublesome persistent symptoms in the clinical setting. However, it is less practical for research projects, firstly because of the cost of obtaining X-rays after fracture union and secondly as it requires the patients to reattend the hospital, even if they are asymptomatic. Most fractures of the little finger metacarpal shaft and neck occur in young men who are notoriously unreliable at attending clinic appointments, especially if they are asymptomatic (Ford et al., 1989; Lowdon, 1986; Theeuwen et al., 1991). Thus, a clinical method for assessing malunion of little finger metacarpal shaft and neck fractures would be a valuable research tool as it would reduce the costs of studies on the influence of malunion on the functional outcome of these fractures and allow patients to be assessed in their homes, which should improve study recruitment. This might improve the quality of research on the outcome of these fractures (Poolman et al., 2005) and clarify whether the biomechanical concerns regarding malunion are clinically relevant (Ali et al., 1999; Birndorf et al., 1997) and the recent interest in operative fixation of these fractures is justified (Al-Qattan, 2006; Faraj and Davis, 1999; Margi This study assesses whether quantitative assessments of the degree of malunion of little finger metacarpal neck and shaft fractures can be obtained by comparing the relative lengths of the ring and little fingers of the injured and contralateral hands of patients.
Finger length measurements The relative lengths of the ring and little fingers of the injured and contralateral hands of patients were measured, first with their metacarpophalangeal joints extended and, then, with them flexed to 90°. Both measurements were performed in a standardised fashion, with the patient seated in front of a table with both shoulders resting by the sides of the body and both elbows flexed to 90°.
The ‘straight metacarpophalangeal (straight-MCP)’ measurement
The ‘90° flexed metacarpophalangeal (90-MCP)’ measurement This was measured to assess palmar displacement of the metacarpal head due to fracture angulation. The hand was placed with the finger metacarpophalangeal joints flexed to 90° over the edge of a table top and the fingers, with the interphalangeal joints extended, lying flat and perpendicular to the table edge on the table top (Fig 3). The difference between the lengths of the ring and little fingers was measured in this position in the right (cr) and left (cl) hands while their metacarpals were pushed against the edge of the table in order to fully extend (and thus standardise) the positions of the ring and little finger carpometacarpal joints. This is important as relative motion can occur between the ring and little finger metacarpal bones at their carpometacarpal joints and extension of the ring finger carpometacarpal joint with flexion of the little finger one would make the little finger appear relatively longer. In this position, a little finger metacarpal fracture which has united with palmar displacement or angulation will cause the little finger to appear relatively longer, such that the difference between its length and that of the ring finger (c) becomes less (Fig 4). In a patient with a unilateral little finger metacarpal fracture, the difference between the lengths of the ring and little fingers in the injured hand and the expected larger reading in the uninjured hand (cr–cl) is represented by "b" in Fig 2 and equates to the amount of palmar shift of the metacarpal head.
Reliability study Fifty subjects with no history of a previous fracture or significant injury to either hand were recruited. There were 18 men and 32 women with a mean age of 38 (range 19–65) years. Forty-five were right-hand dominant. The straight-MCP and 90-MCP measurements were performed on both hands of every subject by the same observer. Both measurements were repeated on the same subjects 1 week later by the same observer, who was blinded to the results of the measurements made 1 week earlier.
Statistical analyses
Responsiveness and validity studies The validity of the two measurements was investigated by comparing their results with the palmar angulation of the metacarpal fracture at presentation and a subjective assessment of cosmesis, which should depend on the severity of the malunion, among other factors. The X-rays of the injured hand (PA and lateral or oblique) which were obtained immediately after the injury were used to measure palmar angulation. Unfortunately, only 77 patients had good quality lateral views. A further 63 had lateral views with some obliquity and 78 had an oblique view (45° rotation of the hand) instead of a lateral view. These were used to estimate palmar angulation as best possible. Fracture angulation was measured on each patient’s X-ray on two occasions, separated by at an interval of 1 week, and the average of these two estimates was used for the analyses. The 95% limits of agreement for these repeat measurements was ±6° and the maximum difference observed between them was 8°. The metacarpal neck fractures were significantly more angulated (median, 34°; range, 21–51°) than the metacarpal shaft fractures (median, 24°; range, 13–42°) (p<0.001, Mann–Whitney). Unfortunately, fracture shortening could not be measured from the X-rays as there were no X-rays of the contralateral, uninjured hand for comparison. The appearance of the healed fracture, which is partially attributable to shortening and angular mal-union (but also attributable to the location of the fracture on the metacarpal, fracture shift and callous formation) was assessed subjectively by the patient using a Likert scale (range 1 – normal, 5 – very unsightly), before the measurements of ring and little finger length were performed.
Statistical analyses
Reliability study The mean difference between the lengths of the ring and little fingers of the dominant hands of the 50 subjects with no history of a previous fracture or significant injury was 25 (SD, 4) mm in the straight-MCP position and 22 (SD, 4) mm in the 90-MCP position. The distributions of both these measurements amongst the study group conformed to normal distributions. Comparison of these length differences between the two hands of each subject showed that the maximum "between side" difference observed in each position was 5 mm.The mean difference for the straight-MCP method was 0.3 (SD, 1.2) mm and for the 90-MCP joint method was 0.2 (SD, 1.6) mm, giving "95% limits of normality" of –2.1 to 2.7 mm and –3.0 to 3.4 mm, respectively. Thus, for clinical purposes, differences of 3 mm or more between these measurements for the right and left hands indicate pathological, rather than physiological, length discrepancies or measurement inaccuracies. The intra-observer reproducibility of both comparisons of finger length (straight-MCP and 90-MCP) was good. The maximum difference between the measurements, taken at an interval of 1 week, was 1 mm for both the straight-MCP and the 90-MCP positions and the 95% limits of agreement were –1.0 to 1.4 mm (straight-MCP) and –0.9 to 1.1 mm (90-MCP). Thus, for clinical purposes, the intra-observer reproducibility for both measurements was ±1 mm.
Responsiveness and validity studies
The cosmesis scores for the neck and shaft fractures were not significantly different (p = 0.8: Mann–Whitney test), but both the straight-MCP (p = 0.01: Kruskal-Wallis test) and 90-MCP (p<0.001: Kruskal–Wallis test) measurements were significantly greater in patients with higher cosmesis scores. The cosmesis score was not influenced by fracture palmar angulation (p = 0.9). Analysis of the cosmesis scores of the neck and shaft fractures separately indicated that, for shaft fractures, the 90-MCP (p<0.001: Kruskal–Wallis test), but not the straight-MCP (p = 0.12: Kruskal–Wallis test), measurement was significantly greater in patients with higher cosmesis scores. In contrast, for the neck fractures, the straight-MCP (p<0.04: Kruskal–Wallis test), but not the 90-MCP (p = 0.17: Kruskal–Wallis test), measurement was significantly greater in patients with higher cosmesis scores.
This study has demonstrated that comparison of the relative lengths of the ring and little fingers of both hands in both the straight-MCP and 90-MCP position can be measured by an experienced observer with an accuracy of ±1 mm. The difference between the relative lengths of the ring and little fingers of both hands is less than 3 mm in 95% of normal subjects. The fracture patients in this study showed increased differences which would be consistent with fracture shortening (straight-MCP measurement) and malunion with palmar angula-tion or shift (90-MCP measurement). These results suggest that both measures are responsive to change, and thus might be clinically useful. However, the validity of both measurements is uncertain as we were unable to correllate either with the palmar angular deformity of the fracture on the X-rays obtained on presentation to the hospital with the acute fracture. As no attempts were made to reduce any of these fractures, one certainly would have expected the 90-MCP measurement to have correlated with palmar angulation of the fracture, but it is possible that some fractures displaced further after the X-rays had been taken. This might have been a result of most patients being encouraged to use and exercise their hands immediately, before fracture union had occurred, and to return to work as soon as pain allowed. Alternatively, our failure to demonstrate a correlation between the 90-MCP measurements and palmar angulation of the fracture might be due to inaccuracies in the measurement of the palmar angular deformity because of the poor quality of some of our lateral X-rays or the use of oblique views in some cases, as these have been shown to overestimate the deformity by up to 35° (Lamraski et al., 2006). However, no correlation between the 90-MCP measurements and palmar angular deformity was found when only the 77 patients with good quality lateral views were assessed and, contrary to the findings of some (Leung et al., 2002) but not others (Lamraski et al., 2006), our reproducibility study suggested that the measurement of palmar angular deformity had good intra-observer reproducibility. Unfortunately, it was not possible to assess fracture shortening as there were no comparative X-rays of the normal hand (Theeuwen et al., 1991). So, we cannot state whether the straight-MCP position measurements accurately reflect longitudinal shortening due to the fracture. In contrast to our measurements of palmar angulation, our assessments of cosmesis were performed after fracture union and consolidation had occurred and, thus, may better reflect the final alignment of the fractures. The cosmetic assessments were worse in the patients with greater differences between the straight-MCP and 90-MCP measurements of their injured and contralateral hands. Therefore, these two measurements may reflect malunion, despite the failure to demonstrate an association with palmar angulation of the acute fracture. Separate analysis of the shaft and neck fractures suggest that cosmetic deformity is principally due to palmar angular/shift malunion for the shaft fractures and fracture shortening for the neck fractures. Although it is generally accepted that shaft fracture malunion causes more cosmetic deformity than neck fracture malunion, this was not demonstrated in our study, probably because the shaft fractures in our study group had less angular deformity than the neck fractures: shaft fractures with greater angular deformity would have been reduced non-operatively (closed reduction and immobilisation in a hand cast) or would have undergone operative treatment and, thus, would not have been recruited to this study. In conclusion, though reliable and responsive, the validity of our two clinical assessments of malunion of fractures of the little finger metacarpal is uncertain. However, on the assumption that cosmesis is influenced by malunion, both measurements appear to quantify some aspects of malunion. A further investigation with good quality, standardised PA and lateral radiographs of the injured and contralateral hands taken after fracture consolidation would be required to fully assess their validity.
This research was funded by the Wishbone trust. Manuscript received March 29, 2006. Accepted for publication September 21, 2007.
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Journal of Hand Surgery (European Volume), Vol. 32, No. 6,
641-646 (2007) This article has been cited by other articles:
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Abstract
MATERIALS AND METHODS
