Z-osteotomy for uniplanar femoral shaft deformity correction in an adolescent with osteogenesis imperfecta

Abstract

Osteogenesis imperfecta (OI) is commonly associated with fragility fractures. It is due to abnormality in the quantity and quality of collagen type 1 caused by mutations in COL1A1 and COL1A2 genes. Patients with OI would also have blue sclera, ligament hyperlaxity, dentinogenesis imperfecta, hearing abnormality, and short stature. Surgical management is preferred to conservative treatment in long bone fractures. For malunited fractures, Sofield-Millar or multiple osteotomies at different sites of deformities are performed with additional intramedullary device to stabilize the bone. This is a case of femur fracture with multilevel CORAs in an adolescent patient with post-trauma OI in which z-osteotomies were performed and stabilized with titanium elastic nails resulting in good outcomes clinically and radiologically.

Introduction

Osteogenesis imperfecta (OI) is a heterogenous group of inherited collagen-related disorder.^{1, 2, 3, 4, 5, 6, 7, 8} It is characterized by bone fragility that commonly results in fracture, growth retardation, and deformity.¹ Fracture rates decline significantly as patients attain skeletal maturity.^1,4 However, approximately 25% of osteogenesis imperfecta-related fractures occur in adulthood.¹

Sofield-Millar operation is widely accepted method among surgeons to correct multilevel deformities in malunited long bone fractures among patients with OI.^{9, 10, 11, 12} A wedge of bone is removed from the osteotomy sites, and closing wedge method is always preferred to opening wedge to avoid nonunions and need for bone grafting.^11,12 A z-osteotomy is one of the options for deformity correction.¹³ However, up to date, the use of z-osteotomy technique in patients with OI is still limited. Thus, we would like to report a case of an adolescent patient with OI who had femoral shaft fracture with preexisting deformity that subsequently underwent multilevel corrective osteotomies with z-osteotomy technique and stabilized with titanium elastic nails (TENS). This technique is relatively easy to learn and would enable the surgeons to correct uniplanar multilevel long bone deformities utilizing an intramedullary implant without causing damage to the growth plate and articular surface.

Case report

An 18-year-old adolescent male patient, a known case of osteogenesis imperfecta, presented with left thigh pain and swelling after he slipped and fell. He previously had multiple episodes of long bone fractures (Fig. 1a–d). He fractured the left femur 4 times prior to this episode. The first episode was addressed surgically with rush rod and plate, and the third episode was treated with implant removal and insertion of the TEN. The second and fourth incidents were treated nonsurgically. Radiograph showed a deformed proximal femur with incomplete fracture involving anterolateral femoral cortex at the distal third of the femoral shaft and bent intramedullary nail. The lateral view showed no significant deformity (Fig. 1a).

Fig. 1.

(a) The first femur AP and lateral radiographs showed a midshaft fracture at the first CORA and the second CORA at the proximal third of the femur with TENS nail in situ (b) The immediate radiograph of the femur after the surgery showing the two CORAs have been corrected with z-osteotomies and fixed with 2 TENS nails and further protected with a full length lower limb cast (c) Radiographs of the femur 6 months after the surgery showing the correction was maintained and the osteotomy sites have already united (d) The osteotomy sites had united and the correction was sustained without evidence of implant failure (nail migration) 2 years after surgery.

The patient was put in supine position with a sand bag placed on the left buttock. After the surgical field cleaned and prepared, the old TEN was removed. A skin incision made at anterolateral aspect of the mid-thigh at the level of fracture site (distal CORA). For our case, we propose a five steps z-osteotomy to correct a uniplanar long bone deformity. The steps can be simplified into five steps: (1) Middle transverse osteotomy, (2) Upper transverse osteotomy, (3) Vertical osteotomy, (4) Extended vertical osteotomy and lastly (5) Lower transverse osteotomy. First, a middle transverse osteotomy is performed using an oscillating saw along the horizontal fracture line, from lateral to medial cortex, perpendicular to the axis of the distal femoral shaft (Fig. 3a). Second, the upper transverse osteotomy for the upper horizontal limb was made in reference to the line perpendicular to the axis of the femoral shaft, proximal to the CORA, from the lateral cortex of the femur stopped halfway at the center of the bone (Fig. 3b). Third, a vertical osteotomy is performed, started from the end of the osteotomy line of the upper horizontal limb extended distally until it touched the midpoint of the transverse osteotomy line (Fig. 3c). The lateral bone wedge then removed (Fig. 3d). Fourth is the extended vertical osteotomy whereby the vertical osteotomy line is continued distally at the distal femoral shaft until the length was about the same with the length of the first vertical limb (distal to CORA) (Fig. 3e). Fifth, a lower transverse osteotomy was then made from the end of the vertical limb extended medially until the end of the medial cortex, and the medial bone piece was removed (Fig. 3f). Completion of the z-osteotomy would correct the deformity at the CORA similar to the angle measured during preoperative templating (25°). This osteotomy would produce two wedges of bones; lateral proximal cortex and medial distal cortex (Fig. 2d). The two resected bone wedges were removed, enabling a closing wedge osteotomy reproduced at each side of the cortex with correction of the coronal alignment (Fig. 3g). The step-by-step description on how to perform a z-osteotomy is described using a simple five-step approach as shown is Fig. 4.

Fig. 3.

A step by step description of the five steps z-osteotomy for the patient. The dotted white line represents the osteotomy described in each photo (a) The first osteotomy was a complete middle transverse osteotomy from lateral cortex to the medial cortex of the femur (dotted white line). The line of the osteotomy was perpendicular to the axis of the distal part of the femur forming the CORA (b) For the upper transverse osteotomy, the line of the second osteotomy was marked with 2 k-wires. The direction would follow the line perpendicular to the axis of the proximal part of the femur forming the CORA. The osteotomy started from the lateral cortex and stopped halfway at midpoint of the bone (dotted white line) (c) Third, a vertical osteotomy at the end point of the second osteotomy was performed until it touched the first transverse osteotomy line (dotted white line). Completion of the first three osteotomies would produce a floating bone wedge at the lateral site (white x mark) (d) The bone wedge was then removed (e) Fourth step is the extended vertical osteotomy (white line). The length of the distal vertical osteotomy should be similar to the proximal vertical osteotomy length. Fifth is the lower transverse osteotomy that started at the end point of the vertical osteotomy and it was extended until the medial cortex (dotted white line). This would produce a floating medial bone wedge (white x mark) which was removed (f) after all the osteotomies were completed and the floating bone wedges were removed, the proximal and distal femur segments were reduced and the deformity at the CORA was straightened.

Fig. 2.

(a) Pre-operative planning of the deformed femur model was performed. The two CORAs were addressed by performing lateral close wedge osteotomies. (b) The model of the post-corrected femur after the lateral corrective osteotomies and reduction have been performed with a nail as internal stabilizer. (c) The two CORAs identified at the mid shaft and proximal third of the femur. The lateral closed wedge osteotomy was mapped onto the radiograph as planned in the femur model (d) The pre-operative z-osteotomy planning for the two CORAs prior to osteotomies and reduction. The black line represents the osteotomies while the white x marks are the floating lateral and medial bone wedges that are removed after the completion of the osteotomies. The step-by-step explanation of the osteotomy procedure are explained in Fig. 3 (e, f) The end result after the z-osteotomies were completed for both CORAs producing a straight femur with two TENS nails in situ.

Fig. 4.

(a) and (b) A step-by step diagram on how to perform five steps z-osteotomy. The CORA is identified. (1) The first step is a middle transverse osteotomy (1 = solid line) from lateral to medial cortex following a line perpendicular to the axis of the distal part of the femur. (2) The second step is upper transverse osteotomy, made from the distal cortex and directed medially halfway until the midpoint of the bone (2 = round dot). The direction is perpendicular to the axis of the proximal femur forming the CORA (3) Third step is a vertical osteotomy from the point end point of the previous osteotomy until the first osteotomy line (3 = square dot). This will produce a floating bone wedge laterally (white x). (4) Fourth, is the extended vertical osteotomy, whereby the osteotomy line is continued distally (4 = thin line) (4) Fifthly is the lower transverse osteotomy from the end point of the previous osteotomy and is directed medially towards the medial cortex (5 = compound line). The line of osteotomy should be perpendicular to the axis of the distal part of the femur forming the CORA. This will produce a floating bone wedge medially (black x). (c) Completion of these osteotomies would remove two bone wedges. Opposition of the proximal and distal segments will result in correction of the deformity.

Another anterolateral skin incision was made at the proximal thigh at the level of proximal CORA and similar steps performed to create z-osteotomy and realigned the deformity. The distal and proximal canal at both CORAs were enlarged using rigid reamer to facilitate TENS insertion. The two 4.0 mm TENS were inserted via retrograde method to stabilize the osteotomies and high groin cast was applied after wound closure (Fig. 2e and f). The immediate radiograph was taken postoperatively (Fig. 1b). There were no intravenous bisphosphonates administered to the patient before and after the surgery.

Patient was put nonweight bearing with crutches (NWBC) for a few months until sign of union, clinically and radiographically at 4-month follow-up. Plain radiograph showed good union (Fig. 1c), and the fixation was maintained until 2 years after surgery (Fig. 1d). At 2 years of follow-up, the patient was able to walk unaided with good hip and knee function and return to his previous occupation (Fig. 5). Patient consent for inclusion in study was obtained.

Fig. 5.

(a–d) The assessment of the range of motion of the knee performed after 2 years of surgery. The flexion-extension was 5–100° on both non weight bearing and weight bearing position.

Discussion

Osteogenesis imperfecta is a rare metabolic bone disorder characterized by type 1 collagen abnormality in which about 80–95% of the cases are inherited as autosomal dominant.^{1, 2, 3, 4, 5, 6, 7, 8} They are usually caused by abnormality COL1A1 and COL1A2 genes leading to either qualitative or quantitative defect of collagen type 1. The prevalence of this disease is 1; 10,000.² Its presentations can be divided into skeletal and extra skeletal manifestations. Bone deformity, fragility fractures, ligament laxity, and stunted growth are the skeletal phenotypes, while the extra skeletal manifestations include blue sclera, hearing impairment, dentinogenesis imperfecta, vascular fragility, cardiovascular and central nervous system complications.^{1, 2, 3, 4} The earliest classification system was introduced by Sillence et al. in 1979.^3,4 The classification divides OI into four types based on the pattern of inheritance, presence of blue sclera, fracture deformity, and presence of hearing defect. Type V was added to the classification, and additional subtypes for each type with variable severity and morbidity were included.

The treatment of OI can be divided into medical and surgical management. The aim of medical therapy is to treat painful bone disease, minimizing the incidence of bone deformity, and reducing risk of fragility fractures by optimizing the bone strength. Patients with OI are encouraged to have optimal daily vitamin D and calcium intake as well. Those with moderate severity need to avoid strenuous physical activity to reduce fracture risk. Occupational therapy has proven benefits for patients who have limited function due to upper limb deformity.³ The use of bisphosphonates is believed to have significant effect in improving bone mineral density, reducing the incidence of fragility and atypical femur fractures and reshaping of the vertebral fractures in children.^3,4,8

Patients would also have problems with multiple episodes of fractures complicated with bone deformities. OI type III and IV are more susceptible to long bone fractures, but nonunions are observed mostly in patients with OI type IV who received conservative treatment.⁷ Most surgeons prefer surgical management in treating long bone fractures in patients with OI as nonsurgical treatment is more prone to nonunions.⁷ However, surgical treatment is very challenging due to the underlying metabolic bone problems and the anatomical abnormalities.⁷ The goals of the surgery are to correct the existing deformity, fix the bone with an intramedullary device, and prevent future refracture and nonunion.⁸ Theoretically, intramedullary device is a better option since it provides mechanical stability, less stress directed to the bone upon surgery, optimal load transfer capability, minimal operative soft tissue handling, preservation of periosteal blood supply (especially when it was performed with minimally invasive percutaneous osteotomy) and shorter period of postoperative immobilization.⁷

The intramedullary device that used for stabilization in patients with OI can be divided into nontelescopic device such as rush rods, TENS, and Kirschner wires, whereas the telescopic type includes interlocking rods, Bailey-Dubow, Fassier Duval, and Sheffield rods. Generally, telescoping rods have better union rates and patients’ mobility status as well as lesser incidence of bony rod outgrowing and rod breakage, refracture and reoperation rate.⁹

Sofield-Millar operation is the most popular method to correct malunion via multilevel osteotomies in order to realign the preexisting deformities combined with insertion of rigid intramedullary rods to provide stable internal support.^9,11 Some authors had suggested modifications in this technique to improve the outcome of the surgery. However, complications such as malunion, refractures, recurrence of the deformity, decrease in the bone width, and rod migration still occurred that necessitate further surgery.¹¹ To minimize the complications, the authors suggested to keep the osteotomies as minimal as possible, at least two or less. The osteotomy should be performed via smaller incisions, and if possible, the incised periosteal tissues must be sutured back to preserve the blood supply.^11,12

There were a minimal number of reports about z-osteotomy technique in deformity correction of a long bone especially in patients with OI. The z-osteotomy technique was described in a unilateral Blounts disease of a 5-year-old child.¹³ The authors suggested that it was a reliable technique to correct both angular and rotational deformity simultaneously. After 2 years, there was no documented complication, and the corrected angular and rotational deformity of the proximal tibia was maintained.¹³ In 2019, a malunited humeral shaft fracture was treated with rotational osteotomy with good outcome 1-year postsurgery. However, this case was complicated with transient radial nerve injury that recovered well with conservative treatment.¹⁴

In our case, we believe that z-osteotomy has a few advantages. After 4 months, the osteotomy sites achieved union, and at 2 years recent follow-up, the patient had good outcome functionally and radiologically. The configuration of the osteotomy enables the deformity to be corrected in a better unidirectional translational stability (coronal orientation) as well as rotational stability. Furthermore, it enables the osteotomized site to have larger surface and contact areas after reduction was obtained thus promoting better bone healing. In adolescents, an intramedullary nail was preferred for a femur fracture. However, in patients with OI with a femur fracture, intramedullary nail insertion is a challenging surgery. As bone in patients with OI is fragile and prone to fracture, we decided not to use solid intramedullary nail. In this case, the deformity correction was held using TENS. Unlike the intramedullary nail insertion, by placing TENS, surgeons can avoid injuring the growth plates if the surgery is performed in patients who still have remaining growth potentials. Furthermore, medullary canal of patients with OI is often small in diameter with thin and sclerotic cortices that could potentially lead to difficulty in nail advancement. Iatrogenic fractures can also be avoided especially at femoral neck during intramedullary nail insertion. The use of TENS nails in femur fracture stabilization is not a famous practice in late adolescent patient, but it is really working well in this case with good outcome radiographically and clinically. As bone fragility is a concern, TENS nail is one of the good alternatives in patient with OI after multi-level corrective osteotomies in femur if other type of fixation is not suitable. For our case, after a 2 year follow up, the patient has satisfactory outcome, good range of motion of the hip and knee, well healed scar, no episode of surgical site infection, united osteotomy with maintenance of the correction both clinically and radiologically. In conclusion, we propose this technique as good alternative to correct multilevel uniplanar long bone deformity as it is simple, easily understandable, utilizing a flexible TENs nail that can accommodate small medullary canal with thick bone cortex, has good short and long term radiological and clinical outcome and enables the surgeon to avoid injury to the growth plate and articular surface if it is performed in skeletally immature patients.

Disclosure of competing interest

The authors declare that they have no confict of interest.