This study examined the tibial component alignment in similar groups of patients, in terms of patient demographics, who were treated by a group of four surgeons. The intramedullary guide was found to be more reliable for determining coronal alignment. Use of the extramedullary guide seemed to more reliably cut the desired posterior slope but the difference was only one degree. Regardless of which alignment jig was used, this did not seem to influence patient outcome.
Component alignment has been shown to have a bearing on patient outcome parameters. When analysing alignment parameters such as sagittal femoral, coronal femoral, rotational femoral, sagittal tibial, coronal tibial and femuro-tibial mismatch, this group found that when the number of alignment errors were reduced that the short term patient outcomes were significantly improved . Use of the intramedullary jig seems to reduce the chance of outliers. This is one of the proposed benefits of navigated TKA . However, computer navigated total knee arthroplasty has been found not to be a cost effective investment in terms of reducing revision risk in TKA .
A study of British orthopaedic surgeons found that 75.6% prefer extramedullary and 20.3% prefer intramedullary jigs when determining tibial alignment with the remainder using both or neither . The published literature is divided as to which jig is superior. Rottman et al found no difference in alignment between intra- and extramedullary alignment in TKA in a retrospective series of 55 patients . Reed et al performed a randomised prospective trial which showed that intramedullary guides were superior to extramedullary guides in determining coronal alignment of the tibial component . In this study, we also found that the intramedullary guide was more reliable in determining coronal alignment. The mean deviation from the mechanical axis was 1.6 degrees with this jig but more importantly, there were no outliers.
There are relative indications for each method of alignment determination. Lozano et al examined obese patients and found no difference in the alignment of the tibial component between intra and extramedullary guides. However, there was a reduced tourniquet time associated with the intramedullary guide . However, transesophageal echocardiography during the course of conventional intramedullary instrumented total knee procedures has demonstrated showers of fat or intramedullary embolic particles enter the right atrium of the heart in repeated and unpredictable patterns . Most often these are clinically unimportant. Patients with significant extra-articular deformities, marked bowing, and those with prior surgery or fractures may not be suitable for intramedullary guides, and they may require the use of extramedullary guides and intra-operative radiographic control .