O’Brien v Lochab: Recognized Complications, Factual Disputes, and the Limits of Negligence

A surgical complication is not the same thing as surgical negligence. A patient who suffers a known risk of a procedure has had something happen that the medical literature predicted would happen to some proportion of patients. The fact that the patient is the one in whom the risk materialized does not, by itself, establish that anything was done wrong. The framework is sometimes counterintuitive for patients and families because the consequences of the complication can be substantial, and the human instinct is to attribute serious consequences to someone’s failure. But the law does not equate consequences with fault. The law requires proof of a breach of the standard of care and proof that the breach caused the harm. Where neither is established, the case is dismissed regardless of the severity of the outcome.

O’Brien v Lochab, 2025 ONSC 2046, released by the Ontario Superior Court of Justice on April 2, 2025, is a recent application of the framework in the orthopaedic surgery context. The plaintiff was a 68-year-old woman who suffered a hip fracture, underwent a partial hip replacement, experienced subsidence of the prosthesis several weeks later, and required revision surgery to a total hip replacement. She alleged that the original surgery had been negligently performed because the surgeon had not adequately addressed what she contended was a more extensive fracture than the surgeon recognized. The court found that the surgeon’s evidence about the fracture’s extent was credible, that it was corroborated by the pre, intra, and postoperative X-rays, that the standard of care had been met, and that the subsidence was attributable to a recognized complication of uncemented hip prostheses (failure of osteointegration) rather than to any negligence. The action was dismissed with partial indemnity costs to the defendant.

The case is doctrinally important for several reasons. It is one of the clearest recent articulations of the recognized complication framework in the orthopaedic context. It illustrates the dynamics of expert disagreement that turns on a contested factual premise rather than on the underlying medical principles. It addresses the weight given to the operating surgeon’s contemporaneous observations when corroborated by imaging. And it adds the first orthopaedic surgery decision to the developing cluster of recent Ontario malpractice trial authorities.

The clinical context — hip fractures and hip replacement

A brief clinical overview is useful for the analysis.

Hip fracture types. The hip is the joint between the head of the femur and the acetabulum of the pelvis. Fractures involving this region are classified by their anatomical location:

• Femoral neck fractures — through the narrow region between the femoral head and the broader part of the upper femur (the trochanteric region). These fractures often disrupt the blood supply to the femoral head, which can lead to avascular necrosis (death of the bone tissue) if the head is preserved. In older patients with displaced femoral neck fractures, partial or total hip replacement is typically preferred over fixation precisely because of the avascular necrosis risk.
• Intertrochanteric fractures — through the region between the greater and lesser trochanters of the upper femur, below the femoral neck. These fractures preserve the femoral head’s blood supply but disrupt the mechanical structure of the upper femur. They are typically treated with fixation devices (sliding hip screws, intramedullary nails) rather than with replacement.
• Subtrochanteric fractures — below the lesser trochanter, in the upper shaft of the femur. These fractures are also typically fixed rather than replaced.

The location of the fracture matters because it determines the appropriate surgical approach. A femoral neck fracture in an older patient is generally an indication for hip replacement. An intertrochanteric fracture is generally an indication for fixation with a hip screw or nail. The choice of surgical approach depends on the correct identification of the fracture type.

Hip replacement options. Where hip replacement is chosen, several options are available:

• Partial hip replacement (hemiarthroplasty) — only the femoral side of the joint is replaced. The acetabulum is left intact. The prosthesis includes a stem that sits in the upper femur and a head that articulates with the patient’s native acetabulum. This is faster surgery and is often chosen for older patients with femoral neck fractures.
• Total hip replacement (total hip arthroplasty) — both sides of the joint are replaced. The acetabulum receives a shell (typically with a polyethylene liner) and the femoral side receives a stem and head as in the partial replacement. This is more extensive surgery but typically has better long-term outcomes for active patients.

Cemented vs uncemented prostheses. Within hip replacement options, the femoral stem can be fixed to the bone in two ways:

• Cemented stems — bone cement (polymethyl methacrylate) is used to fix the stem to the inside of the femur. The cement bonds to the prosthesis and grips the bone, providing immediate fixation.
• Uncemented stems — the stem is press-fit into the femur without cement. The prosthesis has a textured or porous surface designed to encourage bone ingrowth (osteointegration) over time. Initial stability depends on the mechanical press-fit; long-term stability depends on the osteointegration that develops over the weeks and months following surgery.

The Biomet Taperloc stem used in O’Brien v Lochab is an uncemented prosthesis designed for osteointegration.

Osteointegration and subsidence. Osteointegration is the biological process by which bone tissue grows into the porous surface of an uncemented prosthesis to create a stable, biological fixation. The process unfolds over weeks to months following surgery. During the initial period, the prosthesis depends on the mechanical press-fit for stability.

Where the osteointegration process fails to establish stable fixation, the prosthesis can sink (subside) into the femoral canal under the patient’s weight-bearing load. Subsidence can produce leg-length discrepancy, pain, and altered hip biomechanics. The literature on uncemented hip prostheses recognizes subsidence as one of the principal failure modes, with reported failure rates in the range of approximately 5 percent (the figure both parties accepted in O’Brien v Lochab).

Subsidence is not a one-cause phenomenon. It can be associated with:

• Patient-related factors (bone quality, body mass, activity level, smoking, certain medications)
• Surgical-technique factors (positioning of the stem, undersizing of the stem, inadequate press-fit)
• Implant-related factors (specific stem design, surface treatment)
• Postoperative factors (early weight-bearing, falls, infection)

The distinction between subsidence attributable to negligence and subsidence attributable to recognized complication risk is precisely the question that frequently arises in orthopaedic malpractice cases.

Reinforcing cables. Where the femur has a fracture or where the surgeon is concerned about the integrity of the femoral cortex during stem insertion, small metal cables (cerclage cables) can be placed around the femur. The cables can serve two purposes: therapeutic (to reduce and stabilize a fracture that the surgeon has identified) or prophylactic (to protect the femur against potential fracture during or after stem insertion). The distinction between therapeutic and prophylactic use is part of the technical record.

The facts

The fall and presentation. On Christmas morning 2018, the patient fell at home. She was 68 years old. The fall resulted in a hip injury. She was transported by ambulance to the Thunder Bay Regional Health Sciences Centre, where X-rays confirmed a fracture in the right femoral neck.

The initial assessment. The initial assessment underestimated the extent of the fracture. The full extent was subsequently appreciated. The defendant orthopaedic surgeon, with a medical resident, determined that the fracture was displaced and that surgery would be required.

The surgical decision. The patient consented to a partial hip replacement. The plan involved an uncemented Biomet Taperloc femoral stem, selected for its design characteristics including the intended osteointegration.

The surgery. During the operation, the defendant identified features of the fracture that required adjustment in the surgical approach. The choice of the Taperloc stem remained unchanged. To reinforce the femur and reduce the risk of further fracturing or instability, the defendant used small metal cables. The exact number and placement of these cables, and whether they were therapeutic or prophylactic, became central to the dispute at trial.

The postoperative course. Immediately after surgery, the patient’s recovery was described as promising. She was discharged with standard hip replacement aftercare instructions. In early January 2019, she began to experience pain and a limp. A February 2019 follow-up assessment revealed that the prosthesis had subsided. The subsidence had produced a leg-length discrepancy.

The revision surgery. Consultations led to a second operation. The procedure was a conversion to a total hip replacement using a long-stem modular system with a permanent acetabular shell. The revision surgery was successful.

The action. The plaintiff brought a civil action against the defendant orthopaedic surgeon alleging that the original surgery had been negligently performed because the actual fracture had been more extensive than the surgeon recognized, that this had led to an inadequate surgical response, and that this in turn had caused the implant subsidence and the need for revision surgery.

The factual dispute at the heart of the case

The case turned on a factual question: what was the actual extent of the fracture at the time of the initial surgery?

The plaintiff’s position. The fracture was more severe than the defendant recognized. It extended below the calcar (the dense bone supporting the femoral neck and head) into the lesser trochanter region. This made it an intertrochanteric fracture rather than a pure femoral neck fracture. The use of three cables reflected the extensive nature of the fracture. The fracture was inadequately addressed because:

• The Taperloc stem was too short for the extent of the fracture
• A longer stem would have been required to bridge the fracture and provide adequate stability
• The osteointegration depended on stable initial fixation, which the short stem could not provide given the extent of the fracture

The defendant’s position. The fracture did not extend beyond the upper cable position, which was above the lesser trochanter. The fracture was therefore a femoral neck fracture rather than an intertrochanteric fracture. The additional cables were used prophylactically to protect the femur against possible fracture during stem insertion, not therapeutically to address an actual fracture extending below the calcar. The defendant based this evidence on:

• His direct intraoperative observations of the fracture
• Pre-operative X-rays showing the fracture pattern
• Intraoperative X-rays taken during the surgery
• Postoperative X-rays showing the stem position and any fracture lines

The acknowledged background. Both parties accepted that uncemented prostheses such as the Taperloc have a recognized failure rate in the range of approximately 5 percent. The defendant’s position was that the patient fell within this recognized minority. The plaintiff’s position was that the failure was attributable to negligence rather than to the background failure rate.

The expert evidence

Both sides called expert evidence on the standard of care and on the underlying clinical questions.

The plaintiff’s experts. The plaintiff’s experts supported the position that an intertrochanteric fracture had existed, that it had been inadequately addressed by the use of a shorter stem, and that the inadequate surgical response had caused the implant failure.

The defendant’s expert evidence. The defendant’s evidence emphasized:

• The intraoperative observations of the surgeon
• The radiographic evidence available throughout the patient’s care
• The recognized failure rate for uncemented prostheses
• The clinical pattern of subsidence as consistent with the recognized complication rather than with a surgical technique failure

The dynamic of the expert disagreement. The expert disagreement was not principally about the underlying medical principles. Both sides accepted the relevant orthopaedic literature, the role of osteointegration, the recognized 5 percent failure rate, and the general principles of hip replacement surgery. The disagreement was about the factual premise: what did the X-rays actually show, and what did the surgeon actually see?

This pattern of expert disagreement is doctrinally significant. Where experts agree on the medical principles but disagree on the factual premise, the case turns on the resolution of the factual question. Once the factual question is resolved, the expert opinion that was built on the rejected factual premise collapses with it.

The court’s findings

The court found in favour of the defendant. The reasoning proceeded in several steps.

The defendant’s evidence was credible. The court found that the defendant orthopaedic surgeon had provided credible evidence about the location and extent of the fracture. The defendant’s testimony about his direct intraoperative observations was treated as reliable.

The radiographic evidence supported the defendant. The court found that the pre, intraoperative, and postoperative X-rays supported the defendant’s account of the fracture’s location and extent. The radiographic evidence was the contemporaneous record of the fracture pattern. The X-rays did not show the extensive intertrochanteric fracture pattern that the plaintiff’s experts had identified.

The plaintiff’s experts misunderstood the fracture location. The court characterized the plaintiff’s experts’ disagreement as a misunderstanding of the fracture location, not a different interpretation of the underlying medical principles. Once the factual premise was resolved against the plaintiff (the fracture was where the defendant said it was, not where the plaintiff’s experts had read it to be), the plaintiff’s experts’ opinion that the fracture had been inadequately addressed no longer rested on a sustainable foundation.

The standard of care was met. With the factual question resolved, the court found that the defendant had met the standard of care for the surgery and for the discharge instructions. There was no breach of duty in the conduct of the operation or in the postoperative care.

The subsidence was a recognized complication. The court found that the femoral device’s subsidence was attributable to a known risk of osteointegration failure rather than to any negligence. The patient was in the approximately 5 percent of cases in which the recognized complication had materialized.

The disposition. The action was dismissed. Partial indemnity costs were awarded to the defendant. The partial indemnity costs framework is the standard framework for costs awards in unsuccessful civil claims in Ontario, reflecting the rule that the unsuccessful party typically bears a portion (though not all) of the successful party’s legal costs.

The legal framework — recognized complications and the standard of care

The case engages several established legal frameworks.

The standard of care framework. The standard of practice for an orthopaedic surgeon is that of a reasonable orthopaedic surgeon in similar circumstances. The framework is the same as for other medical specialists (Wilson v Swanson, [1956] SCR 804; ter Neuzen v Korn, [1995] 3 SCR 674). The standard is not perfection. The standard does not require the surgeon to anticipate or prevent every complication. The standard requires the surgeon to exercise the skill and care that a reasonable specialist in the field would exercise.

In orthopaedic surgery, the standard of care includes:

• Appropriate pre-operative assessment and diagnosis
• Appropriate surgical planning including choice of approach and implant
• Appropriate intraoperative execution including adaptation to findings
• Appropriate postoperative care including weight-bearing instructions and follow-up

The framework permits a wide range of acceptable approaches. Where reasonable surgeons would differ on the technical decisions (which stem to use, whether to use cables, what fixation approach to take), the framework does not select between them. The framework asks whether the chosen approach falls within the range of acceptable practice.

The recognized complication framework. Where a patient suffers a known complication of a procedure and the complication occurs within its typical rate, the complication does not by itself establish negligence. The framework operates as follows:

• The procedure has known risks documented in the medical literature
• The risks materialize in some proportion of patients regardless of the standard of care exercised
• A patient in whom the risk materializes has experienced an unfortunate but predicted outcome
• Negligence requires more than the materialization of a known risk; it requires proof that the specific case was caused by a breach of the standard of care rather than by the recognized risk

The framework is doctrinally important because it preserves the boundary between bad outcomes and culpable conduct. Without it, every adverse outcome would support a malpractice claim, which is neither what the law requires nor what the medical literature describes.

The factual dispute resolution framework. Many medical malpractice cases turn on factual disputes about what actually happened or what was actually observed. The court’s role is to resolve these factual disputes on the balance of probabilities, applying the rules of evidence and the principles of credibility assessment. Where the resolution favours the defendant, the case fails at the factual level before any analysis of the legal standard of care.

The expert opinion as derived from facts framework. Expert opinion in medical malpractice is built on factual premises. Where the factual premise is contested and the court resolves it against the side whose expert relied on that premise, the expert opinion built on the rejected premise loses its evidentiary value. This is not a criticism of the expert; it is a feature of how expert evidence functions in a fact-finding court.

The contemporaneous documentation framework. Where the contemporaneous documentation (operative notes, radiographic studies, postoperative records) supports one party’s factual account, the documentation can be decisive. The framework reflects the broader principle that contemporaneous records are typically more reliable than after-the-fact reconstruction or interpretation.

The doctrinal anchors

Several doctrinal anchors emerge from the case.

The “recognized complication versus negligence” framework. Where a known risk of a procedure materializes within its typical rate, the materialization does not establish negligence. The framework is one of the most doctrinally important defendant-favourable frameworks in medical malpractice law. O’Brien v Lochab applies it specifically to uncemented hip prosthesis subsidence with a 5 percent failure rate.

The “expert disagreement based on factual misunderstanding” framework. Where one side’s experts proceed from a different factual premise than the other side’s experts, the court must resolve the underlying factual question first. If the factual premise is resolved against the side whose experts relied on it, the expert opinion built on that premise collapses. O’Brien v Lochab illustrates the framework in operation: the plaintiff’s experts’ opinion rested on the premise that the fracture extended into the lesser trochanter; the court rejected that premise; the expert opinion did not survive.

The “intraoperative observations plus radiographic evidence” framework. Where the operating surgeon’s direct intraoperative observations are corroborated by pre, intra, and postoperative imaging, the combination of evidence carries substantial weight. The framework is generalizable across surgical specialties where intraoperative findings are routinely documented and where radiographic evidence is available.

The osteointegration failure framework. Uncemented hip prostheses depend on osteointegration for long-term stability. Failure of osteointegration is a recognized complication occurring in approximately 5 percent of cases. The complication is not, by itself, evidence of surgical error. O’Brien v Lochab is the principal cluster authority on the framework.

The orthopaedic standard of care framework. The standard of care for orthopaedic surgeons follows the general specialist standard. The framework permits a wide range of acceptable technical approaches. O’Brien v Lochab is the first orthopaedic decision in the cluster.

The “expert opinion built on rejected factual premise” framework. Expert opinion does not survive the rejection of its factual foundation. The framework is generalizable across medical malpractice cases where the technical opinion depends on a contested factual premise.

The partial indemnity costs pattern. Unsuccessful plaintiffs in Ontario medical malpractice cases typically bear partial indemnity costs awarded to the successful defendant. The framework reflects the broader rule that the unsuccessful party typically bears some portion of the successful party’s costs. O’Brien v Lochab applies the framework in the orthopaedic context.

The contemporaneous documentation as fact-finding anchor framework. Where contemporaneous documentation (operative notes, radiographic studies, postoperative records) supports one party’s account, the documentation can be decisive. The framework is generalizable across medical malpractice cases.

The defendant trial-win cluster. O’Brien v Lochab joins the growing cluster of recent defendant trial wins in medical malpractice. The cluster illustrates the principle that the standard of care framework does not equate adverse outcomes with negligence.

Why this case matters

For prospective plaintiffs and families. The case is an important illustration of the structure of medical malpractice law.

Some practical observations:

A bad outcome does not equal negligence. Many surgical complications occur in patients whose surgeons did everything within the standard of care. The medical literature documents specific complications and their typical rates. Where a patient experiences a recognized complication at its expected rate, the case is unlikely to succeed regardless of how serious the consequences are.

The framework operates particularly clearly in orthopaedic cases. Orthopaedic procedures (hip replacement, knee replacement, fracture fixation) have well-documented complication profiles. The recognized complications include subsidence of uncemented stems, loosening of fixation, infection, dislocation, periprosthetic fracture, and others. Each has a documented typical rate. Cases that fall within these rates are particularly difficult to litigate successfully.

The factual premise matters. Medical malpractice cases often turn on what the records, imaging, and contemporaneous documentation actually show. Where the records support the defendant’s account, the case becomes much harder to advance. The candid evaluation of the records before commencing litigation is critical.

Expert opinion is essential but not conclusive. Expert opinion in malpractice cases is built on factual premises. If the underlying premise is contested and the court accepts the other side’s premise, the expert opinion built on the rejected premise loses its weight. This is one reason why early and careful evaluation of the records is essential before deciding whether to advance a malpractice claim.

Costs are a real consideration. Unsuccessful plaintiffs typically bear partial indemnity costs awarded to the successful defendant. The financial consequences of an unsuccessful malpractice claim can be significant. The framework reinforces the importance of careful evaluation before commencing litigation.

For more on the general framework for evaluating these cases, see Why Many Medical Malpractice Cases Are Declined in Ontario and Suing for Medical Malpractice in Ontario: What You Need to Know.

For surgeons and surgical teams. A few practical observations:

Document the intraoperative findings. Where the surgeon’s account of the intraoperative findings is the principal evidence on a contested question, the contemporaneous operative note is the primary record. The note should be detailed, specific, and timely. The combination of detailed operative notes and radiographic evidence is the foundation of the surgeon’s evidence.

Document the rationale for technical choices. Where the choice of approach or implant is contested at trial, the contemporaneous reasoning is the principal record of the standard of care analysis. The reasoning should be evident from the records.

The framework protects reasonable practice. The standard of care framework protects reasonable orthopaedic practice. Surgeons who exercise reasonable judgment, document their decisions, and provide appropriate care are protected by the framework even where the outcomes are adverse. The framework is not a guarantee against litigation but does provide the foundation for a successful defence where the care was within the standard.

Postoperative monitoring matters. Even where the surgery has been performed appropriately, the postoperative monitoring framework supports early identification of complications. Subsidence can be detected on follow-up imaging before the patient becomes symptomatic. Early identification supports earlier intervention.

Cluster integration

This is a defendant trial win, joining the developing cluster of recent defendant-favourable orthopaedic and surgical malpractice decisions. For other recent defendant trial-win cases, see the related case comments on Pellerin v Mistry, Sutherland v Encompass Health, Williamson v Y, Papineau v 1428581 Ontario Ltd, Noel v Lakeridge Health, Lorencz v Saskatchewan Health Authority, Yang v Freed, Graham v and McMullan v.

For the broader framework on declined malpractice cases, see Why Many Medical Malpractice Cases Are Declined in Ontario. For the foundational principles, see Most Common Misunderstandings About Medical Malpractice in Ontario.

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Decision Date: April 2, 2025

Jurisdiction: Ontario Superior Court of Justice

Citation: O’Brien v Lochab, 2025 ONSC 2046 (CanLII)

Outcome: Judgment in favour of the defendant orthopaedic surgeon. The court dismissed the plaintiff’s claim and awarded partial indemnity costs to the defendant. The court found that the defendant had met the standard of care in performing a partial hip replacement following a femoral neck fracture, including the technical decisions about implant selection, the use of reinforcing cables, and the postoperative discharge instructions. The court accepted the defendant’s evidence about the location and extent of the fracture, which was corroborated by the pre, intraoperative, and postoperative X-rays. The court characterized the plaintiff’s experts’ opinion that the fracture extended into the lesser trochanter as based on a misunderstanding of the fracture location rather than a sustainable alternative interpretation of the imaging. With the factual premise rejected, the plaintiff’s experts’ opinion that the fracture had been inadequately addressed by the chosen surgical approach no longer rested on a sustainable foundation. The court found that the subsidence of the prosthesis was attributable to a recognized complication of uncemented hip prostheses (failure of osteointegration), which occurs in approximately 5 percent of cases, rather than to any negligence by the defendant.

Key authorities: Wilson v Swanson, [1956] SCR 804 (standard for specialists); Crits v Sylvester, [1956] OR 132 (standard of care for medical practitioners); ter Neuzen v Korn, [1995] 3 SCR 674 (specialist standard and common practice as defence).