Bilateral Sagittal Stress Fracture of Distal Femur Secondary to Osteoarthritis Knee: A Report on Unusual Case

Abstract

Introduction

Stress fractures in the sagittal plane of the distal femur are rarely observed in clinical practice, particularly when occurring as a consequence of advanced knee osteoarthritis. This case report aims to highlight a rare presentation of sagittal plane stress fractures in the distal femur resulting from advanced knee osteoarthritis. It discusses the implications of this condition for both diagnosis and treatment, underscoring the need for heightened clinical awareness in patients with severe degenerative joint disease.

Case Presentation

A 74-year-old female presented with bilateral osteoarthritis of knee Kellgren and Lawrence (KL) grade IV with a linear sagittal stress fracture of the distal femur. Unusual type of stress fracture was suspected on plane radiograph and confirmed on Magnetic Resonance Imaging (MRI). Bilateral total knee replacement was performed and screw augmentation was done for stress fracture. On one-year follow-up, patient was symptom-free, with no pain complaints. Knee range of motion was possible up to 0–100 degrees on the bilateral knee joint with no extensor lag.

Discussion and Conclusion

Bilateral sagittal stress fractures of the distal femur secondary to osteoarthritis of the knee represent a rare but clinically significant pathology. Surgical intervention, by total knee replacement with adjunctive measures to stabilize the fractures, can effectively alleviate pain and improve functional outcomes in these patients.

Level of Evidence

V.

Introduction

Asymmetrical loading and inappropriate repetitive stress concentration in the metaphyseal area of the proximal tibia or distal femur can result in insufficiency stress fractures when Osteoarthritis (OA) of the knees is accompanied by coronal deformities such as varus or valgus [1]. The underlying osteoporotic bone in this group of older patients exacerbates this [2]. In early OA, greater loads are transferred to the medial compartment as lateral femoral bending proceeds, and denuding of cartilage is frequently observed in the middle and posterior portions of the medial condyle [3]. The mechanical strength of the distal femur in advanced OA varies by area and may be higher in the middle and posterior regions of the medial condyle, leading to stress fracture [4].

Most case studies on stress fractures of the proximal and even distal tibia are currently found in the literature [1, 5, 6]. Also, there is research on the on stress distribution in advanced osteoarthritis in the distal femur [7]. The existing literature includes a single case report documenting a stress fracture in the distal femur [8]. However, current literature is still lacking on the studies including, sagittal stress fractures in the distal femur caused by advanced OA. This case report aims to highlight a rare presentation of sagittal plane stress fractures in the distal femur resulting from advanced knee osteoarthritis. It discusses the implications of this condition for both diagnosis and treatment, underscoring the need for heightened clinical awareness in patients with severe degenerative joint disease.

Case Presentation

A 74-year-old female presented to the outpatient department with complaints of pain in the bilateral knee, difficulty in weight-bearing, and restricted movement for five years. The patient initially developed pain in the medial aspect of the knee joint, which was more prominent when walking uphill and downstairs. Later, she developed generalized pain over the knee along with an increase in varus deformity of the knee. Since the last three months, the severity of the pain has increased, and the patient has had difficulty walking, even for household work.

At presentation, the visual analog scale (VAS) score for pain in the right knee was 9/10, and on the left knee was 8/10 on bearing weight. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score was 17 for pain, 5 for stiffness, and 54 for physical function, with a total WOMAC score of 76 on the right knee. Whereas 14 for pain, 4 for stiffness and 54 for physical function, with a total WOMAC score of 72 over the left knee. Oxford Knee Score (OKS) of 12 on right knee and 15 on left knee. The patient walks on a walker with mild flexion deformity of the knee and varus thrust gait bilaterally. There was diffuse swelling over the bilateral knee joint. On palpation, the swelling was soft to firm in consistency, with deep tenderness over the medial joint line and medial aspect of the distal femur bilaterally on deep palpation. There was flexion deformity of the knee 15 degrees on the right knee and 10 degrees on the left knee. Knee range of motion was further possible up to 80 degrees on the right knee and 90 degrees on the left knee, with tenderness on a whole range of motion associated with patellofemoral crepitus. Varus and valgus stress tests at both 0 degrees and 30 degrees were negative on the bilateral knee. Distal neurovascular status was intact.

Investigation

Bilateral knee plain radiographs revealed a gross decrease in medial and lateral knee joint space, with advanced arthritic changes on the knee joint and moderate to large osteophytes. There was also a noticeable varus deformity at the knee with stress fracture starting from the intercondylar notch and extending proximally towards the diaphysis of the femur, as shown in Fig. 1. Magnetic Resonance Imaging (MRI) revealed reduced space in the bilateral knee with gross arthritic changes and osteophytes on the bilateral tibial and femoral condyles. There was also a linear fracture with adjacent mild callus formation extending from the intercondylar notch of the bilateral femoral condyle to distal femoral diaphysis with surrounding marrow and soft tissue oedema, as shown in Fig. 2. The final diagnosis of bilateral osteoarthritis of knee Kellgren and Lawrence (KL) grade IV with a linear sagittal stress fracture of the distal femur was made.

Fig. 1.

Plain radiographs of bilateral knee anteroposterior standing and lateral view, showing gross decrease in medial and lateral knee joint space, with advanced arthritic changes on the knee joint and moderate to large osteophytes, along with noticeable varus deformity at the knee with stress fracture starting from the intercondylar notch and extending proximally towards the diaphysis of the femur

Fig. 2.

Pre-operative MRI knee; A: Right side; B: Left side; Showing reduced space in the bilateral knee with gross arthritic changes and osteophytes on the bilateral tibial and femoral condyles. There was also a linear fracture with adjacent mild callus formation extending from the intercondylar notch of the bilateral femoral condyle to distal femoral diaphysis with surrounding marrow and soft tissue oedema

Surgical Procedure

With due informed consent from the patient, bilateral total knee replacement was planned. An orthopaedic team led by a consultant arthroplasty surgeon performed the surgery. The patient was positioned in a supine, and a standard medial parapatellar incision was given on the bilateral knee. Bilateral total knee replacement was performed using posterior stabilized implants. A long-stem tibial component was used on the right side. In the same setting, the stress fracture was addressed using compression screws from medial to lateral configuration. Two compression screws were used on the right side, and one compression screw was used on the left side.

Due to the sagittal plane orientation of the fracture, compression screws were selected over alternative fixation options such as locking plates or buttress plates. Compression screws provide direct compression across the fracture site, promoting stability and optimizing the healing environment. Furthermore, they have a lower profile and occupy less area within the distal femur, which is particularly advantageous when planning for total knee replacement. This approach minimizes interference with the TKR implant placement, facilitating a more precise and stable joint reconstruction.

In our case scenario, the decision to use a stemmed tibial component on the right side and a non-stemmed component on the left was based on specific clinical considerations. The right tibia exhibited signs of osteopenia, necessitating the added stability provided by a stemmed component to ensure adequate load distribution and minimize the risk of implant loosening. Additionally, the right knee may have had anatomical deformities that required a more secure fixation, whereas the left knee displayed favorable bone quality and anatomy, allowing for the effective use of a non-stemmed component. This approach was tailored to optimize stability, enhance postoperative recovery, and align with the patient's overall rehabilitation goals.

Outcome

The postoperative period was uneventful. Immediate postoperative plain radiographs showed a bilateral posterior stabilized total knee replacement implant in place with a long stem tibial component on the right side, as well as two compression screws on the right side and one on the left side in place, as shown in Fig. 3. The patient was on non-weight-bearing mobilization in a wheelchair on postoperative day 1. Intravenous Zolendronic was given a 5 mg dose to increase the bone quality. Patient was discharged on the fourth postoperative day. On discharge, the patient was kept on a low dose pulsatile dose of Teriparatide 20 mcg daily for three months. Sutures were removed at two weeks’ follow-up after adequate surgical site healing. At two weeks follow-up, no complications were seen. Patient was maintained on strict non-weight bearing mobilization for six weeks. Partial weight-bearing mobilization was started on a six-week follow-up. There was adequate union present at the stress fracture site at three months’ follow-up, as shown in Fig. 4. During the one-year follow-up, the patient was symptom-free, with no complaints of pain. Knee range of motion was possible up to 0–100 degrees on the bilateral knee joint with no extensor lag, as shown in Fig. 5. The patient can do all household work comfortably and carry community ambulation. On one-year follow-up, the right knee WOMAC score was 6 for pain, 2 for stiffness, and 24 for physical function, with a total WOMAC score of 32 for the right knee. Whereas 5 for pain, 2 for stiffness and 24 for physical function, with a total WOMAC score of 31 over the left knee. OKS of 38 for the right knee and 40 for the left knee.

Fig. 3.

Immediate postoperative plain radiographs showing bilateral posterior stabilized total knee replacement implant in place with a long stem tibial component on the right side, as well as two compression screws on the right side and one on the left side in place

Fig. 4.

Three-month follow-up plain radiograph showing bilateral posterior stabilized total knee replacement implant in place with adequate union present at the stress fracture site

Fig. 5.

One-year follow-up clinical image showing knee range of motion was possible up to 0–100 degrees on the bilateral knee joint with no extensor lag

Discussion

Stress fractures are defined as fractures that result from recurrent micro trauma to the bone over an extended period of time [9]. It falls into two categories: insufficiency fractures and fatigue. Fatigue fractures occur when normal bones experience persistent abnormal stress. An aberrant underlying bone under normal force will not fracture sufficiently [10]. The fracture is not acute because the insults are typically mild and persistent in nature. The most common locations for stress fractures in the lower extremities are the femoral neck, tibial diaphysis, metatarsals, and calcaneus. Particularly in the patella, proximal tibial and fibular metaphyses, femoral condyles, and supracondylar distal femur, stress fractures are less common in the region surrounding the knee [11].

The existing literature only reports stress fractures in the proximal and distal tibia, which are secondary to osteoarthritis [5, 6]. However, we could not find any case that reported a stress fracture in the distal femur, which has a pattern of the sagittal split of the medial condyle. This paper presented a case of osteoarthritis of bilateral knee KL grade IV with bilateral sagittal split stress fracture of the distal femur medial condyle.

Osteoarthritis stress fractures are primarily caused by coronal deformities such as varus or valgus deformity, which cause the mechanical axis to shift away from the knee and uneven load distribution in the proximal tibia and distal femur [4]. This abnormal repetitive stress concentration occurs in the metaphyseal area of the proximal tibia and distal femur [4]. Greater stress is placed on the proximal tibia medial pleasure and distal femur medial condyle in patients with varus mal-alignment [3]. This stress is further exacerbated by sagittal abnormalities in moderate-to-severe arthritis. The major biomechanical element involved in the aetiology and healing of these stress fractures is determined by the coronal plane alignment [1].

Diagnosing a stress fracture around the knee may be challenging. Palpable discomfort and localised pain due to compression are physical indicators of a stress fracture [12]. Considering the proximity of the stress fracture to the knee joint, the doctor may investigate intraarticular or periarticular pathology [13]. When knee discomfort and limited mobility first appear, doctors may think about more prevalent problems like osteoarthritis or meniscal injuries. Tumours, bursitis, mechanical causes, and tendinitis are further differential diagnoses that could exist [14].

In the majority of cases reported in the literature, plain radiographs are used to diagnose stress fractures. However, plain radiographs may show no abnormalities in the early stages [9]. MRIs and bone scans can aid in diagnosis in questionable situations [15]. A stress fracture might be suspected in individuals with severe osteoarthritis if their pain over the proximal tibia worsens suddenly [13]. To find the stress fracture, full-length and serial radiographs are required [15]. Differentiating sagittal stress fractures of the distal femur from other periarticular or intraarticular diseases that are frequently linked to knee discomfort is one of the main diagnostic problems [14]. Nonetheless, the diagnosis of stress fractures can be aided by the persistence of pain in spite of conservative treatment and the distinctive results of imaging tests, such as MRIs and plain radiography.

It can be difficult to treat these stress fractures conservatively or surgically [14]. Conservative care consists of electrical stimulation, immobilisation with a cast, and non-weight bearing alone. Numerous instances that were treated conservatively and reported in the literature later developed non-union or pseudoarthrosis, which was accompanied by persistent malalignment and worsened osteoarthritis symptoms [3]. These individuals eventually needed surgery. Osteoarthritis-related malalignment raises the stress at the fracture site, increasing the risk of delayed or non-union.

A distinct surgical difficulty arises when managing bilateral sagittal stress fractures of the distal femur in the context of advanced osteoarthritis. For the alleviation of pain and restoration of function in end-stage knee osteoarthritis, total knee replacement (TKR) continues to be the gold standard treatment [1]. In this instance, further steps were made to stabilise the stress fractures while TKR was used to treat the underlying arthritis. To promote fracture healing and avoid displacement, an innovative way to augmenting the fixation of fractures is the use of compression screws [16].

The postoperative phase is essential for monitoring the patient's progress and ensuring optimal outcomes [16]. In this instance, the surgical treatment was effective and the patient experienced no acute consequences. To promote healing, postoperative rehabilitation techniques were used. These included medication-assisted bone quality enhancement and non-weight-bearing mobilisation [17]. During follow-up visits, the patient showed good improvement, showing signs of fracture union on radiographs and showing notable improvements in pain scores and functional results.

Maintaining bone mineral density and preventing further fractures are difficult aspects of managing osteoporosis. The current standard of care for treating osteoporosis is the use of bisphosphonates [18]. An annual intravenous dose of 5 mg of Zoledronic acid is authorised for the treatment and prevention of postmenopausal osteoporosis, as well as for the augmentation of bone mass in males who already have osteoporosis [19]. Teriparatide administration promotes the growth of new bone, which increases bone density and strength. In individuals with osteoporosis, Teriparatide injections have been shown to be an effective means of increasing bone mass and lowering the risk of fracture [20]. In this instance, osteoporosis has been treated using a combination intravenous Zolendronic acid followed by low dose pulsatile Tereperatide.

This case presents a unique instance of bilateral sagittal stress fractures in the distal femur’s medial condyle secondary to advanced osteoarthritis, contrasting with other stress fracture cases primarily documented in the proximal tibia and distal tibia, as noted in existing literature. Unlike this case, previous reports—such as the study by Bhattacharjee et al.—describe intraarticular stress fractures associated with osteoarthritis affecting different anatomical regions or involving only one side of the knee. Bhattacharjee's report of a 53-year-old male with severe osteoarthritis detailed a left medial femoral condyle fracture, treated with total knee arthroplasty and osteosynthesis, highlighting the complexity of intraarticular fractures. On the thorough search of literature, no documented cases feature a sagittal split pattern stress fracture of the distal femur’s medial condyle bilaterally, as in this patient. Furthermore, in this case, compression screws were innovatively employed alongside a bilateral posterior-stabilized total knee replacement to stabilize the fractures, which differs from conventional treatments in literature that often involve conservative approaches or single knee arthroplasty. [8]

This report describes a 74-year-old female patient with bilateral advanced osteoarthritis that has increased in intensity over the last three months as a result of a stress fracture, leading to functional restriction. To treat a sagittal stress fracture, the patient underwent a successful bilateral posterior stabilised complete knee replacement with compression screw augmentation. This example emphasises how crucial it is to rule out stress fractures when making a differential diagnosis for knee discomfort, particularly in elderly persons who may have underlying osteoarthritis. When a patient presents with unusual symptoms or persistent pain, clinicians should be on the lookout for stress fractures. To minimise problems and improve patient outcomes, early detection and effective treatment are essential.

This case presents limitations primarily associated with the patient's osteoporosis, which negatively impacts fracture healing and overall outcomes. Osteoporosis increases the risk of delayed union or non-union of fractures, complicating recovery despite surgical intervention. The treatment regimen, including intravenous zoledronic acid and low-dose pulsatile teriparatide, aimed to enhance bone density, but individual responses may vary. Furthermore, the patient's age may contribute to slower healing rates and higher postoperative complication risks. The presence of advanced knee osteoarthritis introduces mechanical malalignment, further complicating the healing process by imposing abnormal loading on the distal femur. These factors highlight the need for a multidisciplinary approach in managing such cases and emphasize the importance of ongoing research into the interactions between osteoporosis and knee osteoarthritis to optimize treatment strategies and improve patient outcomes.

Future research should focus on the relationship between osteoporosis and the development of stress fractures in the context of knee osteoarthritis, exploring optimal treatment strategies to enhance fracture healing. Additionally, studies examining the efficacy of various osteoporosis management protocols in conjunction with surgical interventions for stress fractures could provide valuable insights. Understanding the biomechanical factors contributing to stress fractures in this population may also inform preventative measures and improve clinical outcomes. A multidisciplinary approach that includes orthopedic surgeons, endocrinologists, and rehabilitation specialists will be essential in addressing the complexities of managing these patients effectively.

Conclusion

To conclude, key takeaways for practitioners from this case emphasize the critical importance of vigilance for stress fractures in patients with OA, particularly those in advanced stages and with concurrent osteoporosis. Maintaining awareness of atypical presentations, such as bilateral sagittal stress fractures of the distal femur, is essential for guiding appropriate clinical assessments. Early diagnosis is paramount, as timely identification enables effective imaging and intervention strategies, preventing complications like delayed union or non-union. In cases where surgical intervention is necessary, procedures such as total knee replacement combined with adjunctive measures to stabilize fractures can lead to significant improvements in pain relief and functional outcomes. Ultimately, fostering a proactive approach to diagnosis and treatment will enhance recovery and improve the quality of life for patients affected by OA and stress fractures.

Authors’ contributions

A. R.—Planning of study, writing, and revising the manuscript. J. P.—Planning of study, and writing the manuscript. P. K. – Data Management and revising the manuscript. R. R.—Data Management.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. There is no conflict of interest of any kind with the research or its outcome among the investigators.

Ethical approval

This study was conducted in compliance with the principles of the Declaration of Helsinki.

Consent to Participation

Not applicable.

Informed Consent for Publication

Informed consent was obtained from the patient for publication of this paper. On request, a copy of the written consent is available for review by the Editor-in-Chief of this journal.