Plantar pressure distribution before and after hallux valgus and hallux limitus surgery.

Abstract

Hallux valgus and hallux limitus are two common foot pathologies that may require surgical intervention. While the modified Austin bunionectomy and the Youngswick osteotomy/cheilectomy respectively, are often used to correct these conditions, insufficient research has been published regarding the effects of these procedures on plantar pressure distribution of the foot. This thesis involves a series of six studies investigating topics relating to radiographic measurements and plantar pressure distribution over a two-year period, in normal feet and in hallux valgus and hallux limitus feet before and after corrective surgery.A review of the literature is presented relating to the development of plantar pressure measurement technology, the aetiology and surgical management of hallux valgus and hallux limitus, the reliability of the EMED system used in the studies, and the related clinical uses of plantar pressure measurement.An initial study was designed to investigate the reliability measurements using a simplified two-step method of data collection as compared to the traditional mid-gait technique of ten normal asymptomatic subjects. Intra-class correlation coefficients were calculated and compared for the pressure variables of contact area, contact time, maximum force and peak pressure of ten regions of the foot.A study to determine normal reference range values for the EMED-SF system was then conducted using thirty healthy subjects and the two-step method of data collection. Descriptive statistical reporting of peak pressure, mean pressure and pressure-time- integrals were presented for ten regions of the foot.Three related studies on radiographic and plantar pressure measurement differences, and their relationships were made using thirty normal, hallux valgus and hallux limitus feet. Various angular and linear radiographic measurements were tested for intra-rater reliability of measurement and pressure variables of peak pressure, mean pressure and pressure-time-integral of 10 regions of the foot were recorded and one way analysis of variance employed to assess any significant differences.Finally, two independent two-year prospective studies were designed to investigate the effects of the modified Austin bunionectomy for hallux valgus and the Youngswick osteotomy/cheilectomy for hallux limitus on plantar pressure distribution of the forefoot. In addition, fundamental radiographic measurement changes of the forefoot of hallux valgus subjects and range of motion changes of the first metatarsophalangeal joint of hallux limitus subjects were conducted. Thirty-six healthy volunteers acted as control subjects, 31 subjects (44 feet) with hallux valgus and 17 subjects (23 feet) with hallux limitus were included in the study. Using an EMED-SF system, plantar pressure variables of peak pressure, pressure-time-integral, contact time, maximum force and force-time-integral were recorded at six regions of the forefoot, pre-operation and repeated at three, six, 12, 18 and 24-months post-operation for surgical subjects. Control subjects were tested at zero and 24-months. Descriptive statistics, multivariate and univariate analysis of variance with contrasts, t-tests of significance and correlations between certain measurement parameters were used in the analysis of the results.The findings of these studies suggest that the two-step method of data collection of plantar pressure measurements is more reliable that the traditional mid-gait technique for most pressure variables. Consequently, the two-step method was employed as the preferred method of data collection in this series of studies.With respect to radiographic differences between normal, hallux valgus and hallux limitus, it appears that hallux valgus feet have significant increases in metatarsus primus varus and first metatarsal protrusion distance, while hallux limitus feet have increased hallux abductus interphalangeal angles. Comparison of pressure variables between each group demonstrate hallux valgus feet have a medial localisation of peak pressure beneath the first, second and third metatarsal heads, suggesting that hyperpronation of the foot is associated with the development of hallux valgus. Hallux limitus feet on the other hand, show increased pressure beneath the hallux, third and fourth metatarsals and lesser toes, indicating a more lateral locus of pressure loading, suggestive -of the foot functioning in a more supinated position. No significant relationship was found between any radiographic parameter and pressure variable tested in either group of subjects.Plantar pressure measurement changes show the greatest variation during the initial three to six months following surgical treatment of hallux valgus and hallux limitus. The Youngswick osteotomy/cheilectomy for the treatment of hallux limitus produces near-normal range of motion of the first metatarsophalangeal joint. Pressures of the first metatarsal head remain relatively constant over the period of measurement, while a significant reduction of the hallux and lateral metatarsals were noted, related to increased dorsiflexion of the hallux. Pressures of the second metatarsal head remained significantly above pre-operation levels. The modified Austin bunionectomy for the treatment of hallux valgus produced 24-month radiographic changes consistent with accepted values. Pressure variables of the hallux reduced to normal values, with the first metatarsal head demonstrating an initial significant decrease and subsequent increase by twelve months post-operation to remain with the second metatarsal head at relatively similar values to pre-operation measurements.The research demonstrates the two-step method of data collection is a viable means of obtaining reliable plantar pressure measurement data in the clinical situation. The investigations into radiographic and plantar pressure distribution indicate that structural radiographic and functional differences exist between normal, hallux valgus and hallux limitus feet. However, no relationship could be found between any of the radiographic parameters and pressure variables tested.The modified Austin bunionectomy for hallux valgus significantly reduced fundamental radiographic measurements to accepted post-operative values, while the Youngswick procedure for hallux limitus significantly increased the amount of post-operative dorsiflexion of the hallux to normal values. The research demonstrates that immediate and longer-term functional changes to the forefoot occur following the surgical treatment of hallux valgus and hallux limitus, however plantar pressure measurements do not return to normal values. No correlation was found between plantar pressure measurements and post- operative radiographic measurements in the hallux valgus group. However, the increased amount of dorsiflexion of the hallux post-operatively in the hallux limitus group was correlated with reduced lateral loading of the forefoot. Post-operation changes of plantar pressure distribution indicate that the rehabilitative period required to achieve stable foot function is between twelve to eighteen months. Furthermore, plantar pressure measurement technology offers the clinician a useful tool to monitor foot function prior to and following therapeutic intervention.