Radiostereometric Analysis Useful for Evaluating Healing of Distal Femoral Fractures

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Radiostereometric analysis (RSA) is useful for follow-up after orthopedic surgery because over time it can track minute motion or no motion at all. RSA involves an intraoperative injection of tantalum bead markers into the bone. During follow-up, stereoradiographs are used to determine the location of the markers in three dimensions. The images are analyzed with a software package that calculates any micromotion that's occurred since the previous imaging.

In the field of arthroplasty, RSA is already the gold standard in evaluating the positional changes of prostheses. Past studies have demonstrated the feasibility of using RSA to monitor distal femoral fractures.

Vincent Galea, PhD, clinical research consultant, Marilyn Heng, MD, MPH, orthopaedic trauma surgeon, Charles R. Bragdon, PhD, associate director of clinical studies at the Harris Orthopaedic Laboratory at Massachusetts General Hospital, and colleagues built on that research by conducting a larger prospective study with one-year follow-up. In the Journal of Orthopaedic Trauma, they report that RSA revealed identified cases of fracture nonunion within three months.

Study Methods

The researchers enrolled 20 adults with a distal femoral fracture that was treated by locked lateral plating at Massachusetts General Hospital. They were evaluated the day after surgery and two, six, 12, 26 and 52 weeks postoperatively. At each study visit, patients completed the Patient-Reported Outcomes Measurement Information System (PROMIS) pain interference and physical function questionnaires. Patients were also evaluated with RSA at each follow-up visit. One set of radiographs was taken with the patient at rest, non-weight bearing, and the other was taken with as much force on the extremity as the patient could tolerate.

The main outcome measurements, measured at each study visit, were:

• Unloaded interfragmentary motion over time: determined by comparing the relative position of the distal fracture segment and the proximal segment at the follow-up visit against the postoperative position
• Inducible micromotion at the fracture site: less difference in distance between the distal and proximal fracture segments before and after loading was interpreted as indicating increased fracture stiffness, and vice versa

Cases of Union

Sixteen patients completed the follow-up protocol. Fourteen of them demonstrated radiographic evidence of progressive fragment bridging over the course of follow-up, and they reported improved symptoms.

For these patients, RSA revealed that:

• Unloaded interfragmentary motion was significant between two and six weeks, and between six weeks and three months, but not after three months
• Decreases in inducible micromotion followed the same pattern
• Through the course of the study, patient reports of their symptoms on the PROMIS questionnaires paralleled the increasing fracture stiffness measured by RSA

Cases of Nonunion

Two patients eventually required revision surgery for fracture nonunion. In these patients, there was no stabilization of unloaded interfragmentary motion or decrease of inducible micromotion after the three-month study visit.

One case of nonunion was asymptomatic; in fact, the patient's PROMIS scores were completely indistinguishable from those of the union cohort.

Conclusions

RSA of distal femoral fractures is a suitable outcome measure for studies evaluating the fracture healing process. Professional societies should consider recommending it to providers in clinical settings, especially for follow-up of patients who have both positive and negative predictors of healing.

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