TLEMsafe: Improving safety and predictability of complex musculo-skeletal
surgery using a patient-specifc navigation system. Part IIb: validation with hip patients pre and post OR.

Two of the most challenging surgical interventions on patients with hip
disorders are 1) total hip arthroplasty (THA) for developmental dysplasia of
the hips (DDH), and 2) major revision of a previously implanted total hip
replacement (THR).
In the case of THA for DDH, the centre of rotation (COR) of the hip has
gradually migrated cranially over the years because of lack of acetabular
coverage, and the proximal femur is in varus anteversion position. The largest
difficulties lie in the placement of the COR at the correct anatomical location
and determining the optimal amount of femoral shortening. If these are not
optimal, the ability of the patient to perform basic activities of daily living
(ADL) after surgery may be compromised.
In the case of revision surgery, it is a fact that all total hip implants will
fail in time (Schreurs 1994). The clinical outcome of revision surgery is not
as good as that of primary THA. Revision surgery requires more operation time,
there is more blood loss, the incidence of infection is doubled, there is
increased incidence of dislocation, heterotopic ossifications, penetration and
fractures of femur or acetabulum, there are more nerve lesions, and
complications occur more often. Re-revision surgery has even worse outcome
(Retpen, Varmarken et al. 1992). To make sure that a re-revision does not
become necessary, it is essential that during the revision surgery, the COR is
restored at the most anatomically correct location to avoid additional strain
on the implanted acetabulum and femoral head during ADL.
In both DDH patients and patients that require a revision, a powerful computer
model coupled with a surgical navigation system could be of great help, and
this is exactly the challenge of the TLEMsafe project (TLEM - Twente Lower
Extremity Model). The surgeon would benefit greatly from a pre-planning system
that could show him the effects of several surgical scenarios on post-OR
functionality. To this end, we will use a state-of-the-art musculo-skeletal
(M-S) model of the lower limb which has recently been developed (Klein Horsman
2007). In this model, the ability to perform basic ADL after surgery can be
simulated. In order to simulate ADL after surgery in an accurate manner, the
model first has to be made patient-specific and undergo rigorous validation. In
the first part of the project, healthy-subject-specific M-S models have been
created, which are currently being validated. In the present phase of the
project, we will create and validate patient-specific post-OR M-S models of hip
patients. This is a crucial step towards the construction of a reliable
surgical pre-planning and navigation system.

To create and validate patient-specific post-OR M-S models of the lower limb of
hip patients. The primary goal of this study is to see if the model can
accurately predict how a patient walks after surgery given the pre-OR MRI scan
and accurately recorded pre-OR activities of daily living.

Observational prospective cohort study.

The study procedures are split into identical pre-OR and post-OR parts. Both
parts consist of an MRI scan of the lower limb and a session during which the
patient performs basic ADL. The post-OR part takes place 6-9 months after the
surgery.
Each MRI scan takes about 45 minutes. The scans are made exclusively of the
lower limb. They are painless and not dangerous.
The ADL sessions that patients have to perform before and 6-9 months after
surgery take place in the motion laboratory of the department of
Rehabilitation. These sessions take three to four hours to complete. In these
sessions, 3-D kinematics, ground reaction force measurements, and
electromyography will be employed to measure the patient*s functionality during
ADL such as walking, getting up from a chair, stepping over an obstacle, and
maintaining balance while standing on a moveable platform. We will also perform
maximum strength tests. All of the measurements in the motion laboratory are
regularly performed in this laboratory and are non-invasive and painless. If a
patient anticipates or experiences pain during any of the exercises, that
exercise will be skipped.
Both the MRI scans and the ADL sessions will be scheduled as much as possible
on days that the patient is already at the RUMC for other treatment-related
visits.