Development of heterotopic ossifications after surgical treatment of acetabular fractures can result in considerable functional losses and are among the most frequent, clinically relevant reported complications. Their risk factors and a suitable prophylaxis are still under discussion. Classification of heterotopic ossifications is performed according to Brooker et al1 (▶ Table 20.1).
Class | Description |
I | Islands of bone within soft tissues around hip |
II | Bone spurs in pelvis or proximal end of femur leaving <1 cm between the opposing bone surfaces |
III* | Bone spurs that extend from pelvis or the proximal end of femur, which reduce the space between the opposing bone surfaces to < 1 cm |
IV* | Ankylosis of the hip joint |
* Clinically significant ossifications. | |
The incidence of heterotopic ossifications after surgical treatment of acetabular fractures depends on several factors.
In the literature of the last decades, frequencies of up to 90% are reported.2,3,4,5,6,7,8,9 It has to be considered that completely different patient groups are analyzed regarding demographic data, chosen approach, type of surgical treatment, and type of prophylaxis. Recently, lower rates were reported by Baschera et al.10 In an analysis of 90 patients with different acetabular fractures, overall, 16 patients developed heterotopic ossifications (17.7%). Of these, five had grade I, four had grade II, three had grade III, and four had grade IV ossifications.10
Heterotopic ossifications usually occur within 3 months postoperatively, without any additional growth in the further course.11 Under prophylaxis, no additional ossification growth is observed after discontinuation of the medication.
20.2 Risk Factors
Various risk factors for the posttraumatic/postsurgical development of heterotopic ossifications are reported in the literature.
20.2.1 Approach-related Incidence
Distinction between posterior (Kocher-Langenbeck6), anterior (ilioinguinal6), extended approaches,6,12,13 and their modifications14,15,16,17,18,19,20 is made in analyzing the approach-associated occurrence of heterotopic ossifications.
Kocher-Langenbeck Approach
The Kocher-Langenbeck approach is useful in fractures involving the posterior acetabulum. Soft tissue damage is possible due to the injury itself, as well as due to the surgical trauma.
Without additional prophylaxis, rates of up to 47% were reported,21 with 10–20% being either grade III or grade IV ossifications,5,6,21,22,23 of which approximately 75% were associated with functional impairment.6,21 Reoperations for heterotopic bone removal were sometimes necessary21,24 (▶ Fig. 20.1).
Fig. 20.1 One year postoperative, development of a grade III ossification with restricted joint movement after an associated transverse posterior wall fracture treated using a Kocher-Langenbeck approach. CT evaluation confirms large heterotopic bone formation in the posterior parts of the joint. After radiation, surgical resection was performed with uneventful further clinical course.
Despite prophylaxis with indomethacin, a comparable rate of heterotopic ossifications was observed, however, a clear reduction of grade III and III-IV ossifications was observed.5,6,22,25,26,27,28 A combined prophylaxis with indomethacin and postoperative radiation resulted in no ossifications in a small series of patients reported by Letournel.6
Overall, results were worse when multiple surgeons performed surgery, whereas single-surgeon treatment (analysis of Letournel, Rommens, and de Ridder) showed acceptable rates.
Clinical Relevance
After Kocher-Langenbeck approach, heterotopic ossification rates of up to 50% are reported. Depending on the type of prophylaxis, significant ossifications are expected in 10–20%.
Ilioinguinal Approach
Performing the ilioinguinal approach, no relevant muscular dissection is necessary. The iliopsoas muscle is bluntly mobilized, only the iliacus muscle is subperiosteally dissected. Correspondingly, soft tissue calcifications are less common.
Without prophylaxis, heterotopic ossifications were observed in only 5.5%. Indomethacin prophylaxis avoided ossifications.5,6
The risk potentially increased when an extended ilioinguinal approach was performed, with detachment of gluteal muscles.6,16 Letournel reported a frequency of 55% ossifications without prophylaxis, whereas in two patients with indomethacin prophylaxis no ossifications occurred.6
Clinical Relevance
Following the ilioinguinal approach, the rate of ossifications is negligible. Prophylaxis with indomethacin safely and completely avoids ossifications.
Intrapelvic Approach
The intrapelvic approach is increasingly used in treating acetabular fractures. As no muscle dissection is usually performed, a low rate of heterotopic ossifications is expected. This is supported by recent data on 464 patients with an overall rate of 3.4% (0–16.7%).29,30,31,32,33,34,35,36
Extended Approaches
The extended approaches allow complete visualization of the whole external surface of the iliac wing with a vascular-pedicled gluteal musculature. This theoretically results in a relatively high risk of developing heterotopic ossifications.
Without prophylaxis, Letournel and Johnson observed periarticular ossifications in three-fourths of the cases.5,6 Significant ossifications occurred in nearly 50% of the operated cases. When prophylaxis was performed, the incidence was comparable using indomethacin but a significant reduction of relevant ossifications to 15% was observed.5,6,26,37,38
Various authors reported results after the Maryland modification of the extended iliofemoral approach.38,39,40 Zeichen et al reported on 12 patients with an ossification prophylaxis with indomethacin.38 In 66.7%, heterotopic ossifications occurred, but only one grade III ossification (8.3%) was seen.
Stöckle et al analyzed 34 patients with a combined prophylaxis with indomethacin and radiation.40 The rate of heterotopic ossifications was 32%; 14.7% had grade III or IV ossifications, of which 60% had significant functional limitations.40
Starr et al analyzed the complications after the Maryland approach.39 Their predominant ossification prophylaxis was by means of radiation. Heterotopic ossification occurred in 67.4%. Significant ossifications were found in 4.6%.
After the triradiate approach according to Mears12 was abandoned due to high complication rates,41,42 Kinik et al reported a relatively small rate of heterotopic ossifications in a recent investigation.43
The prophylaxis regimen consisted of 3 months of indomethacin in combination with radiation therapy. Heterotopic ossifications were observed in only in 16.7% with only 6.7% grade III ossifications.43
Clinical Relevance
An extended approach without ossification prophylaxis is stated as obsolete. Even with prophylaxis, significant ossifications were expected in about 10%. A combination prophylaxis with indomethacin and radiation appears to be the most effective regime.
20.2.2 Gluteus Minimus Injury
The traumatic or surgery-related damage of the gluteus minimus muscle seems to be an important cause of heterotopic bone formation, because ossifications were frequently found in this muscle region.44
Without ossification prophylaxis, Rath et al reported a rate of 10.3% significant ossifications after debridement of necrotic parts of the gluteus minimus muscle, comparable to indomethacin prophylaxis studies.
Clinical Relevance
Injuries of the gluteus minimus muscle should be carefully debrided to avoid ossifications. We highly recommend jet-lavage wound cleansing in every case at the end of surgery.
20.2.3 Fracture Type
Only Letournel6 and Johnson et al5 analyzed the influence of the acetabular fracture type on the incidence of heterotopic ossifications.
Letournel reported a low incidence of 3% only for anterior column fractures, whereas all other fracture types showed rates between 15% and 30%.
Johnson et al provided data only for both-column fractures and T-type fractures. Regardless of the prophylaxis, both-column fractures always led to heterotopic bone formation, whereas in T-type fractures more significant ossifications occurred.5
Both analyses did not report on detailed data regarding the chosen approach.
Clinical Relevance
The fracture type does not seem to affect the development of heterotopic ossifications.
20.2.4 Associated Traumatic Brain Injury
Webb et al reported on a possible association between surgical treatment of acetabular fractures, traumatic brain injury (TBI) and heterotopic ossifications.45 A rate of 91% was observed in patients with a Glasgow coma scale < 11 points, of which 61% experienced restriction of their hip range of motion.
Rath et al could not confirm these results.44 Letournel also found no association between the occurrence of ossifications and an accompanying TBI.6 Only an increase of 5% was seen with concomitant TBI from 20.8% to 25.8%.
Clinical Relevance
An accompanying TBI seems to have a questionable effect on the development of heterotopic ossifications.
20.2.5 Other Risk Factors
No association was found between the occurrence heterotopic ossifications and patient age, sex, duration of surgery, blood loss, surgical approach, and/or trochanteric osteotomy. Associated fracture types showed a trend to more frequent development of ossifications and a significant association was observed between grade III and IV ossifications and delayed treatment.3
Both Letournel and Johnson reported similar results comparing patients treated within 3 weeks after trauma and between 3 weeks and 4 months.5,6 The incidence was dependent on additional prophylactic measures. Delaying operative treatment for more than 4 months showed no influence on ossification rates.6
Clinical Relevance
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