Factors that affect the healing index of metacarpal lengthening: a retrospective study

INTRODUCTION

Callotasis lengthening has been used in hand surgery since 1970. The use of distraction lengthening has produced satisfactory results in the management of hand problems such as congenital anomalies, traumatic amputations, burn, and infection sequelae.1-3

Brachymetacarpia is the congenital shortening of metacarpals and usually affects the third, fourth, and fifth digits. Though its exact aetiology is unknown, premature closure of the epiphysis is thought to be involved. The condition may occur sporadically or form part of a syndrome.4

Belusa5 first reported the successful use of callotasis lengthening for brachymetacarpia in a single digit with no serious complications. Metacarpal lengthening may be achieved by one-stage lengthening although more than one procedure may be required to achieve the proposed length in severe cases. Callus distraction is thus preferred because the lengthening process is gradual, regardless of severity.^" It has a high success rate with good cosmetic results and a low rate of complications. A considerably higher complication rate has been reported in the one-stage lengthening technique.7 It is therefore recommended that the use of one-stage lengthening technique be confined to cases with metacarpal shortness of less than 10 mm.7,10 Callus distraction is an appropriate procedure for all levels of shortness because it is safer and less traumatic.1,7,9

There are few studies of digital lengthening in children.4,8,11 In addition, no studies have identified any variables that can explain the wide variation in time needed by different patients for healing or consolidation. We evaluated factors that affect healing index (HI) and consolidation time (CT) of metacarpals following callus distraction and compare our results with previous studies.

MATERIALS AND METHODS

Eight young women (mean age, 18.6 years; standard deviation [SD|, 6.5 years) who underwent callus distraction for lengthening of congenitally shortened metacarpals were studied. 18 metacarpals were lengthened: short metacarpals were bilateral in 6 patients; 4 of whom had associated short metatarsal(s).

The following factors likely to affect healing and consolidation were recorded: age, type of device, distraction rate, and complications (Table 1). The time of healing and consolidation were determined based on postoperative radiographs taken once a week for 4 weeks. The healing index (HI) was defined as the time (days) needed for consolidation per cm of distracted osteotomy site (days/cm).1 Consolidation time (CT) was the time (days) between the end of distraction osteotomy and total consolidation or removal of fixator. The mean HI and CT of 10 previous studies and this study were compared to identify factors that influence HI and CT (Table 2).

In patients with bilateral involvement, each hand was operated on at separate surgeries. Patients (and parents in the case of children aged younger than 16 years) received detailed information about the procedure. Metacarpophalangeal (MCP) range of motion was measured using a goniometer, preoperatively and (S months postoperatively. Surgery was performed under general anaesthesia in 6 patients and regional anaesthesia in 2. An upper extremity tourniquet was applied and the osteotomy site was exposed through a longitudinal incision on thedorsum of the short metacarpal. Seven metacarpals of 2 patients were lengthened using a mini-type semicircular fixator (Mini Ilizarov, Evrenler, Istanbul, Turkey) [Fig.]. A unilateral external fixator (Medo, Med, Istanbul, Turkey) was used in each of 11 metacarpals of 7 patients. Thus in one patient, different tixators were used in each hand. A transverse limited corticotomy of the proximal metaphyseal cortex was preferred.9

Commencing 5 days following surgery, two 0.25-mm distractions were performed daily (0.5 mm/day). The distance of the distraction gap and the alignment of the metacarpal and callus formation were assessed radiographically twice a week for 3 weeks. Thereafter radiographs were taken once a week. Parents were taught to care and dress the pin tract. Cefazolin sodium was used for prophylaxis. In unilateral cases, distraction lengthening continued until the metacarpal was equal in length to the contralateral normal metacarpal. In bilateral cases, the estimated length of metacarpal was calculated using the method of Aydinlioglu et al.12 (First metacarpal=0.67x second metacarpal=0.71x third metacarpal=0.78x fourth metacarpal=0.84x fifth metacarpal). When the proposed length was reached, adequate bony union was confirmed if cortical continuity was present in a total of 3 anteroposterior and lateral radiographs. The distraction device was then removed in an out-patient setting." No immobilisation was noted following removal of the distraction device and all patients were given instructions for a home rehabilitation programme.

The Mann-Whitney U test was used to verify the differences in HI. Spearman correlation analysis was used to determine the correlations. Preoperative and postoperative MCP range of movement was compared using a paired sample (-test. Differences were considered significant when p<0.05.

RESULTS

After a mean follow-up of 23.6 months, no patients reported pain or functional impairment based on their preoperative functional capacity. Ncurovascular problems, angular deformities, delayed union, refracture, and osteomyelitis were not encountered and no osteoarthritic changes were radiographically evident.

The mean extent of lengthening was 16.5 mm (54.6%; SD, 10.2%) of the original mean length of 29.9 mm. No bone grafting was needed as no patient had insufficient callus formation. The fourth metacarpal was the most frequently affected digit (77.8%); the prevalence of short third and fifth metacarpals was 6% and 17% respectively.

Factors that may affect Hl and CT were evaluated (Table 1). Fixation device (unilateral versus circular), pin tract infection, and sex had no significant effect on Hl and CT. No correlation was found between the extent of lengthening and the Hl or CT. The mean HI was 66 days/cm for the third metacarpal, 49 days/cm for the fourth metacarpal, and 47 days/cm for the fifth metacarpal; this difference was not statistically significant.

Younger patients healed faster than older patients. HI differed significantly between patients aged O to 18 years and those aged 19 to 30 years (p=0.002). Review of our results and 9 other studies revealed a linear relationship between patient age and corresponding HI or CT (increasing age being associated with greater HI and CT) and an inverse relationship between distraction rate and HI or CT (faster distraction rates being associated with smaller HI or CT values) [Table 2].

The mean preoperative and postoperative 6 months MCP extension/flexion range was 19.4

Natural growth did not occur during follow-up because the growth plates of the congenital short metacarpals were closed. The lengths of the normal metacarpals at treatment onset were not significantly different from that at final follow-up. Osteotomy was performed whenever premature consolidation developed before the proposed length was reached, as patients often failed to comply carefully with daily lengthening. Pin tract infection developed in 3 patients and resolved with local wound care and oral antibiotics without the need for pin removal.

DISCUSSION

Metacarpal shortening is most commonly caused by congenital factors and frequently seen in third, fourth, and fifth metacarpals.10 There is no universally accepted set of criteria or consensus on the age at which metacarpal lengthening should be performed.12

Brachymetacarpia refers to the congenital shortening of metacarpals, possibly due to premature closure of the epiphysis. Metacarpal epiphyses close between 14 and 21 years of age.13 Thus, age should be taken into account when contemplating callotasis lengthening.1 In our patients, the epiphysis of the short metacarpal was completely closed, but open in the normal metacarpal. Multiple factors appeared to affect the HI and CT, but age was the most important factor that affected both bone healing and epiphyseal closure.

Smith and Gumley14 recommended that for psychological reasons, metacarpal lengthening for brachymetacarpia should be performed between 2 and 4 years of age. Kato et al.1 suggested that callus distraction be performed when patients are 10 to 15 years of age, because callus formation is abundant and the callus consolidates readily; the epiphyseal plate is almost closed. So the necessary lengthening finally required to correct shortening can be appropriately estimated. In addition, patients are well motivated and cire able to safely manage the external fixator. Toh et al.9 found no correlation between age and HI, but reported that complications prolonged the healing time. In our series, a positive correlation between age and HI was found. Older patients needed more time for consolidation and healing.

The recommended optimal distraction rate varies from 0.3 mm/day to 1.5 mm/day.1,3,7-9,11,15,16 Matev2 recommended 1.5 mm/day distraction, but Kato et al.1 and Toh et al.9 advocated 0.3 mm/day and 0.5 mm/day, respectively. CT and HI are strongly correlated, but do not correlate with the distraction rate (Table 2).

A gap of approximately 3 cm can be achieved within 2 to 3 months without the need for bone graft in patients aged between 10 and 14 years.2 Whereas bone graft is required for about 50% of patients aged between 26 and 30 years,2 and is generally advised for persons older than 25 years who require metacarpal lengthening of more than 3 cm.7,15 Similarly, bone graft is recommended in patients who need lengthening of more than 20 mm.9,15 We achieved a mean lengthening of 16.5 mm without the use of bone graft. Lengthening of more than 20 mm may require greater HI and CT (Table 2); the associated risk of fracture at the lengthened callus is also higher.9,15

Limited corticotomy has been advocated when there is a compromised endosteal blood supply, but endosteal blood supply and bone marrow have no effect on consolidation and healing.4 The proximal metaphysis is the site with the best blood supply, and this reduces the time needed for healing and consolidation.9

Careful preoperative planning, secure intraoperative mounting of the external fixator, and sufficient postoperative patient and parental cooperation are essential to avoid complications. Metacarpal lengthening by callus distraction is an appropriate method that achieves adequate lengthening. Healing is faster in younger patients and, if tolerated, surgery can be performed in early childhood. It can also be performed satisfactorily in adults following traumatic amputations. To avoid additional lengthening of normal metacarpals prior to epiphyseal closure, adolescence is the most appropriate time to perform distraction lengthening in congenitally short metacarpals.

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