Hindfoot Alignment in Total Knee Replacement

When carrying out a knee replacement operation one of the goals is to correct any deformity of the leg (bowlegged or knock kneed). The ideal alignment is the mechanical axis, which is a line from the centre of the hip joint to the centre of the ankle. This line indicates how the weight of the body is transmitted to the ground via the leg. Often the planning for a knee replacement uses an Xray which shows the hip, knee and ankle (HKA Xray) so that the mechanical axis can be drawn on. However, the weight of the body goes to the ground from the ankle through the heel. There have been some reports recently suggesting that deformities in the heel can influence the overall leg alignment after a knee replacement; this may affect how successful the surgery is, or how long the knee replacement will last. Therefore it may make sense to take the alignment of the leg including the heel in planning for a knee replacement. The conventional practice to assess the alignment of the heel is a hindfoot alignment view (HAV) Xray. This only shows the foot. Having two separate Xrays means more radiation exposure and makes linking the two alignments very difficult. We propose a single novel Xray extending the HKA Xray to shows hip, knee, ankle and heel (HKAH Xray) enabling measurement of both alignments. This study is to validate the hindfoot alignment seen on the novel Xray with the standard HAV. Patients undergoing a knee replacement will be enrolled. Patients will have both a HKAH and HAV Xray before surgery. The alignment of the heel measured on the HKAH Xray will be compared with the standard HAV to see if it is accurate.