Lower Extremity Complex Ankle/Foot Injury - AMA Guides, Mastery - Learning Through Reviewing

Reviewing the work of other evaluators is often a learning experience. You may learn new approaches that enhance the quality of your evaluations and reports, or you may learn from the challenges (and errors) that others have encountered.

The following is an example.

"Mr. Sam Examinee sustained a severe left ankle injury on July 27, 2021, resulting in a bimalleolar fracture with syndesmosis injury and posterior tibial tendon rupture. After failed conservative treatment, he underwent triple hindfoot arthrodesis, first tarsometatarsal fusion, and gastrocnemius recession in December 2022. He continues to experience chronic pain and limited mobility. Examination revealed ankle plantar flexion limited to 20 degrees with normal dorsiflexion. The hindfoot was fused, and there was 6 degrees of valgus deformity."

A physician provided the following rating:

"I would refer the reader to the Fifth Edition AMA Guidelines, where they can be rated based on Loss of range of motion, and also, he is essentially fused, so I would give him an impairment rating based on the fused subtalar joint. That would be Table 17-31, 0 millimeters would give him a 25% lower extremity rating for his fused subtalar joint, as he has no motion as per Table 17-31, Page 544. In terms of his ankle, he clearly has tibiotalar arthritis with some remaining motion, although it is decreased. This would be a 20% impairment rating as per the same table. In terms of range of motion loss, I would refer the reader to his plantar flexion loss, Table 17-11, Page 537; this would be considered mild. He has 20 degrees compared to the plantar flexion of 60 degrees on the other side. So, that would be 7%. Therefore, he would have for this loss 7% of the lower extremity, and the other two would be 45%; combined, that would be a total of 49% of the left lower extremity."

Questions for  you are:

• How would you rate impairment using the Fifth Edition?
• Is his rating correct?
• If not, what were the errors?
• How would you rate this using the Sixth Edition?
• Is there any significance to the evaluator misnaming the AMA Guides as the AMA Guidelines?

Let’s review this case, focusing on the impairment rating. The full critique first focused on the clinical issues; however, the following specifically deals with the questions about the rating.

In answering the question about misnaming, in reviewing several thousand impairment ratings, we have observed that when the physician misnames the AMA Guides, the rating is typically incorrect. Why is that? Misnaming the book suggests that the person may not be overly familiar with the AMA Guides or may be careless. Always reference the AMA Guides to the Evaluation of Permanent Impairment correctly.

Fifth Edition Rating

We will start by reviewing the rating process using the Fifth Edition, and then we will critique the rating. Following that, we will discuss approaches based on the Sixth Edition. With the Fifth Edition, the process of assessing lower extremity permanent impairment is described in Chapter 17, Lower Extremities (5^th ed., 523-564). The Guides states,

Typically, only one method will adequately characterize the impairment and its impact on the ability to perform ADL" (5^th ed., 527).

A cross-usage chart (Table 17-2, 5^th ed., 526) indicates which methods and resulting impairment ratings may be combined. 

In the footnote to Table 17-2 (5^th ed., 526), the Guides states,

…for items marked with an "X", you should not use these methods together for evaluating a single impairment.

The following approaches were considered:

17.2b Leg Length Discrepancy: Not applicable. This approach is rarely used to assess impairment, unless there is documented significant shortening of the leg due to the injury, in which case Table 17-4 (5^th ed., 528) is applicable.

17.2c Gait Derangement:  This is a stand-alone methodology and is not applicable in this case. Section 17.2c, Gait Derangement (5^th ed., 529), and associated Table 17-5, Lower Limb Impairment Due to Gait Derangement (5^th ed., 529) are rarely used to assess impairment. The Guides states:

Whenever possible, the evaluator should use a more specific method. When the gait method is used, a written rationale should be included in the report. The lower limb impairment percentages shown in Table 17-5 stand alone and are not combined with any other impairment evaluation method. Section 17.2c does not apply to abnormalities based only on subjective factors, such as pain or sudden giving-way, as with, for example, an individual with low-back discomfort who chooses to use a cane to assist in walking" (5^th ed., 529).

In this case, although Dr. Evaluator reported an antalgic gait, more specific methods were used; therefore, those methods are used.

17.2d Muscle Atrophy, 17.2e Manual Muscle Testing:  Dr. Evaluator reported that "he cannot toe walk because of the weakness on the left side." However, he also reported that "bilateral calves are symmetric at 42 centimeters." Table 17-6, Impairment Due to Unilateral Muscle Atrophy (5^th ed., 530), is used to rate atrophy (measurements are compared 10 cm above the patella and at the maximum circumference of the calf) and Table 17-8, Impairment Due to Lower Extremity Muscle Weakness (5^th ed., 532), is used to rate weakness when the finding of muscular weakness is consistent. Since there is no reference to specific muscular weakness and atrophy (which is a more objective finding than strength testing), ratings are not performed for atrophy or muscle testing.

17.2f Range of Motion:

Section 17.2f states:

Lower extremity impairment can be evaluated by assessing the range of motion of its joints, recognizing that pain and motivation may affect the measurements. If it is clear to the evaluator that a restricted range of motion has an organic basis, three measurements should be obtained, and the greatest range measured should be used. If multiple evaluations exist, and there is inconsistency of a rating class between the findings of two observers, or in the findings on separate occasions by the same observer, the results are considered invalid. Figures 17-1 to 17-6 illustrate one method of measuring range of motion in the lower extremity. The ranges listed in Tables 17-9 through 17-14 are examples of mild, moderate, and severe impairments and are to be used as guides. Range-of-motion restrictions in multiple directions do increase the impairment. Add range-of-motion impairments for a single joint to determine the total joint range-of-motion impairments.

Dr. Evaluator reported:

Dorsiflexion of the right ankle is 45 degrees, and of the left is 20 degrees. Plantar flexion is 20 degrees. The inversion on the right side is 45 degrees, and he is immobile and fused on the left side at 0 degrees. Eversion again 0 degrees on the left, on the right side it is 20 degrees. He did not state whether he performed three measurements.

There are deficits in the motion of the ankle and the foot. Section 17.2a, Converting From Lower Extremity to Whole Person, instructs as follows:

If there are multiple impairments within a region (e.g., the toes and the ankle), combine these regional, lower extremity impairments of the foot and convert the combined foot impairment to a whole person impairment. Similarly, when using separate methods on the same region, combine the regional impairments before converting to a whole person impairment" (5^th ed., 528). "To calculate the lower extremity impairment from a specific part impairment percent (e.g., foot), multiply by 0.7. To calculate whole person impairment from a lower extremity impairment, multiply by 0.4. These values are shown in Table 17-3 (5^th ed., 527). 

In this jurisdiction, impairment is expressed as the most distal, e.g., ankle and foot are expressed as foot. He has no ankle motion and has a fused hindfoot.

Ankle motion impairments are obtained from Table 17-11, Ankle Motion Impairment Estimates (5^th ed., 537), and motion impairments for plantar flexion and extension (dorsiflexion) are added at the foot level. Plantar flexion of 20 degrees results in 10% foot impairment. Dorsiflexion is normal.

Hindfoot motion impairments are obtained from Table 17-12, Hindfoot Impairment Estimates (5^th ed., 537); however, in this case, because of the fusion, the impairment for hindfoot is rated by Section 17.2g Ankylosis.

17.2g Ankylosis: Section 17.2g, Joint Ankylosis, is used to rate the hindfoot ankylosis. Section 17.2g states:

An immobile joint is an impairment even when the position of ankylosis is optimal. Malposition in angulation or rotation of an arthrodesed or fused joint increases the magnitude of the impairment. Surgical correction is usually preferable to accepting a significant malposition, but it is not always possible or practical. Impairment estimates for malposition are therefore included for the infrequently encountered individual who is not a candidate for surgical correction. The following text and Tables 17-15 through 17-30 indicate the optimal neutral positions for ankyloses of the lower extremity joints and provide the impairment percentages for ankyloses in those optimal positions. Any variation from the optimal neutral position of any ankylosed joint increases the baseline impairment percent as indicated in the tables. The values listed are for the maximum end of the deformity range. Specific deformities should be rated using interpolation of the ranges in the tables, as illustrated by examples in this section. Multiple malposition deformities of the same joint, i.e., angulation and malrotation, are added, whereas deformities of the different joints are combined using the Combined Values Chart (p. 604). The baseline rating for ankylosis in the neutral position is used only once for each joint (5^th ed., 538).

Foot (Hindfoot, Midfoot, Forefoot) 

For the subtalar part of the foot, the optimal ankylosis position is neutral, or 0°, without varus or valgus. The ankylosis impairment in the neutral position is 4% for the whole person, 10% for the lower extremity, and 14% for the foot. Malpositioning may increase the whole person impairment up to 25%. Varus or valgus malpositioning is estimated in the same way as for the ankle (Tables 17-25 and 17-26).

Dr. Evaluator states, "he has a clear valgus deformity in the involved left foot," however, he does not quantify this. However, he does state, "documentation in the medical records of 6 degrees valgus deformity, which will allow me to rate him." (However, he did not rate him on this basis.)

For the hindfoot, the subtalar part of the foot, ankylosis in the neutral position results in 14% of the foot. Table 17-26 Ankle Impairment Due to Ankylosis in Valgus Position provides additional impairment if the position is 10 degrees or more. However, since his valgus positioning is lower, this has not been added. It is necessary to achieve the threshold of 10 degrees positioning. Therefore, his impairment for the fusion is 14% of the foot.

17.2h Arthritis: There is no documentation of diminished joint space intervals; therefore, this is not applicable.

Section 17.2h, Arthritis, explains the process of rating arthritis for the lower extremities, which is based on narrowing of joint space intervals, rather than on clinical impressions or findings observed at surgery:

Roentgenographic grading systems for inflammatory and degenerative arthritis are well established and widely used for treatment decisions and scientific investigation. For most individuals, roentgenographic grading is a more objective and valid method for assigning impairment estimates than physical findings, such as the range of motion or joint crepitation. While there are some individuals with arthritis for whom loss of motion is the principal impairment, most people are impaired more by pain and sometimes weakness, but they still can maintain functional ranges of motion, at least in the early stages of the process. Range-of-motion techniques are therefore of limited value for estimating impairment secondary to arthritis in many individuals. Crepitation is an inconstant finding that depends on such factors as forces on joint surfaces and synovial fluid viscosity.

Certain roentgenographic findings that are of diagnostic importance, such as osteophytes and reactive sclerosis, have no direct bearing on impairment. The best roentgenographic indicator of disease stage and impairment for a person with arthritis is the cartilage interval or joint space. The hallmark of all types of arthritis is thinning of the articular cartilage; this correlates well with disease progression.

17.2i Amputations: Not applicable.

17.2j Diagnosis-Based Estimates: Specific conditions are rated per Table 17-33, Impairment Estimates for Certain Lower Extremity Impairments (5^th ed., 546-547). In this case, none are applicable.

17.2k Skin-loss: Not applicable.

17.2l Peripheral Nerve Injuries: There is no evidence of peripheral nerve involvement; therefore, this is not applicable.

17.2m Causalgia and Reflex Sympathetic Dystrophy: Not applicable.

17.2n Vascular Disorders: Not applicable.

Final Lower Extremity Impairment

The final rating is based on the ankle motion deficit (10% foot) combined with the hindfoot ankylosis (14% foot), resulting in 23% foot.

John Evaluator, MD, on January 6, 2025, provided the following impairment assessment:

I would refer the reader to the Fifth Edition AMA Guidelines. he can be rated based on loss of range of motion, and also, he is essentially fused, so I would give him an impairment rating based on the fused subtalar joint. That would be Table 17-31, 0 millimeters would give him a 25% lower extremity rating for his fused subtalar joint, as he has no motion as per Table 17-31, Page 544. In terms of his ankle, he clearly has tibiotalar arthritis with some remaining motion, although it is decreased. This would be a 20% impairment rating as per the same table. In terms of range of motion loss, I would refer the reader to his plantar flexion loss, Table 17-11, Page 537; this would be considered mild. He has 20 degrees compared to the plantar flexion of 60 degrees on the other side. So, that would be 7%. Therefore, he would have for this loss 7% of the lower extremity, and the other two would be 45%, combined, that would be a total of 49% of the left lower extremity. 

The value of 49% lower extremity is equivalent to 70% foot, since to convert to lower extremity, you divide by 0.7.

Critique of Rating

Based on the facts provided and the processes defined in the AMA Guides to the Evaluation of Permanent Impairment, Fifth Edition, I respectfully disagree with Dr. Evaluator's assessment. His report was thoughtful; however, he encountered some issues in rating impairment.

He provides a rating based on Table 17-31 for the fusion; however, he does not explain why he used that table. He does not provide the full name of this Table, which is "Table 17-31 Arthritis Impairments Based on Roentgenographically Documented Cartilage Intervals" (5^th ed, 544). This table is referenced in Section 17.2h Arthritis and is used to grade and rate arthritis; it is not used to rate a fused joint. Therefore, his use of this to provide a rating for a fused subtalar joint is not appropriate.

With a fusion, there is no joint space; however, it is not appropriate to rate it as arthritis. Having performed or reviewed several thousand lower extremity ratings, and (humbly) as the Editor of several AMA Guides publications, I have not seen this confusion. However, I can understand how someone could have conceived that this would be a reasonable approach to rate a fusion; however, it is not. This represents a significant error in Dr. Evaluator's methodology. Using the arthritis table for a fusion is not consistent with the AMA Guides methodology. A proper impairment rating would assess the fusion position (optimal or non-optimal) using the appropriate ankylosis tables rather than using cartilage interval measurements from the arthritis table. Therefore, his rating should be disregarded.

Dr. Evaluator provides an adequate clinical basis to rate impairment; however, his impairment assessment failed to adhere to the processes defined in the AMA Guides; therefore, his rating should be disregarded. Using the data provided in his report and in the records, and applying this to the processes we provided in the AMA Guides, the correct rating is 23% foot, not 70% foot (49% lower extremity).

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Sixth Edition Rating

The Sixth Edition bases impairments primarily on the diagnosis. This is true both for the 2008 printing and the 2014 Digital.

Chapter 16: The Lower Extremities is used to assess lower extremity impairments. For evaluation purposes, the lower extremity is divided into three regions (distal to proximal):

• Foot and ankle: from the midshaft of the tibia to the tips of the toes.
• Knee: from the midshaft of the femur to the mid-shaft of the tibia.
• Hip: from the articular cartilage of the acetabulum to the midshaft of the femur.

The principles of assessment are provided in Section 16.1. Impairments are typically based on the diagnosis, with modification of the impairment based on adjustments for function, physical examination, and clinical studies. Diagnoses for the lower extremity are defined in 3 major categories:

• Soft tissue.
• Muscle/tendon.
• Ligament/bone/joint

Section 16.2 Diagnosis-Based Impairment states:

Most impairments are based on the Diagnosis-based Impairment (DBI), where impairment class is determined by the diagnosis and specific criteria; this is then adjusted by non-key factors (grade modifiers) and may include Functional History (FH), Physical Examination (PE), and Clinical Studies (CS). The grade modifiers, or non-key factors, are considered only if they are determined by the examiner to be reliable and associated with the diagnosis. Typically, these other factors will support the class and default grade assignment; however, in some circumstances, a lower or higher grade may be assigned, depending on the specifics of the case.

Alternative approaches are also provided for calculating impairment for peripheral nerve deficits, complex regional pain syndrome, amputation, and range of motion. Range of motion is primarily used as a physical examination adjustment factor and is only used to determine actual impairment values when it is not possible to otherwise define impairment. Ratings based on range of motion or for complex regional pain syndrome cannot be combined with other approaches.

Figure 16-2, Lower Extremity Impairment Evaluation Record, should be completed, or all information on that record should be provided in the impairment rating report. The terms class, default impairment, adjustments, assigned grade modifier, and optional AAOS Lower Limb Score used in the evaluation record are described in detail in this chapter. An example of a completed Lower Extremity Impairment Evaluation Record (Figure 16-13) is provided at the end of this chapter.

Diagnosis-based impairment (DBI) is the primary method of evaluation for the lower limb. Three regional grids, listing relevant diagnoses, are provided in this section, 1 for each region of the lower extremity (foot/ankle, knee, and hip). An impairment will be defined by class and grade. The Impairment Class (IC) is determined first by using the corresponding diagnosis-based regional grid. The grade is then determined using the adjustment grids.

Once the impairment class has been determined, based on the diagnosis, the grade is initially assigned the default value, C. The final impairment grade, within the class, is calculated using the grade modifiers, or non-key factors, as described in Section 16.3. Grade modifiers include functional history, physical examination, and clinical studies. The grade modifiers are used in the net adjustment formula described in Section 16.3d to calculate a net adjustment. The final impairment grade is determined by adjusting the grade up or down from the default value C, by the calculated net adjustment (≤2 to ≥2). The lowest possible grade is A (adjustments less than -2 from the default value C will automatically be considered A), and the highest possible grade is E (adjustments greater than +2 will automatically be considered E). The regional grid is then consulted again to determine the appropriate impairment value for the selected class and grade. Grade modifiers allow movement within a class, but do not allow movement into a different class.

The regional grid is used for two purposes: (1) to determine the most appropriate class for a specific regional diagnosis and (2) to determine the final impairment after appropriate adjustments are made using the grade modifiers.

There are five classes in the diagnosis-based regional grids:

• Class 0: no objective problem.
• Class 1: mild problem.
• Class 2: moderate problem.
• Class 3: severe problem.
• Class 4: very severe problem approaching total function loss.

Subjective complaints without objective physical findings or significant clinical abnormalities are typically assigned class 0 with no ratable impairment.

This process is repeated for each separate diagnosis in each limb involved. In most cases, only one diagnosis in a region (ie, hip, knee, and/or foot/ankle) will be appropriate. If a patient has two significant diagnoses, for instance, ankle instability and posterior tibial tendonitis, the examiner should use the diagnosis with the highest impairment rating in that region that is causally related to the impairment calculation. If an examiner is routinely using multiple diagnoses without objective supporting data, the validity and reliability of the evaluation may be questioned.

Vascular conditions are rated per Section 4.8, Vascular Diseases Affecting the Extremities, and may be combined in the Lower Extremity Worksheet using the Combined Values Chart in the Appendix. The diagnosis of complex regional pain syndrome, CRPS I, previously known as reflex sympathetic dystrophy (RSD), and CRPS II, known as causalgia, must be supported by consistent, objective findings and is rated as explained in Section 16.5.

Steps in Determining Impairment

1. Perform history and examination, and determine if the individual is at MMI.
2. Establish the appropriate diagnosis for each part of the lower limb to be rated.
3. Use the regional grid in the corresponding region to determine the associated class.
4. Use the adjustment grid and the grade modifiers, including functional history, physical exam, and clinical studies, to determine what grade of associated impairment should be chosen within the class defined by the regional grid.
5. Use the regional grid to identify the appropriate impairment rating value for the impairment class, modified by the adjustments as calculated.
6. Combine lower extremity percentages using the Combined Values Chart in the same extremity as appropriate. If both lower extremities are involved, convert impairments to the whole person and combine. (6^th ed, 497-499).

The use of regional grids is explained in Section 16.2a Diagnosed-Based Class Assignment—Regional Grids:

The first step in determining an impairment rating is to choose the diagnosis that is most applicable for the region being assessed. Diagnoses are divided into three categories: soft tissue, muscle/tendon, and ligament/bone/joint. Typically, soft-tissue diagnoses are assigned the lowest impairments, and ligament/bone/joint diagnoses are assigned the highest impairments. As much as possible, impairment values from prior editions were retained, unless adjustments were necessary to more appropriately reflect the impairment or were required because of changes in the methodology. On the basis of the diagnosis and other specific differentiators that may be associated with that diagnosis, the condition is assigned to a specific class in the regional grid.

Reliability of the diagnosis is essential, and the diagnosis should be consistent with the clinical history and findings at the time of impairment assessment. Surgery does not necessarily result in an impairment rating, unless it is a factor that contributes to placing a diagnosis within a class. Surgical intervention is only relevant if it alters the functional status of the condition evaluated at MMI. For example, surgical repair of a torn cruciate ligament can decrease the instability from a higher class to class 0 if the instability is resolved. That the joint has been treated surgically does not result in an add-on value or additional impairment percentage. Impairment ratings are based on the patient's condition at the time of the rating and do not anticipate or account for the possibility of future interventions.

Selecting the optimal diagnosis requires judgment and experience. If assignment to a class is determined by severity of ROM deficit (ie, normal, mild, moderate, severe, very severe), this severity is determined using Sec. 16.7 ROM Impairment. If more than one diagnosis in a region (ie, hip, knee, and/or foot/ankle) can be used, the one that provides the most clinically accurate and causally-related impairment rating should be used; this will generally be the more specific diagnosis. Typically, one diagnosis will adequately characterize the impairment and its impact on ADLs. Certain diagnoses may span more than 1 class; therefore, these diagnoses are associated with specific objective findings on physical examination or clinical studies to ensure placement in the appropriate class.

In the event that a specific diagnosis is not listed in the diagnosis-based impairment grid, the examiner should identify a similar listed condition to be used as a guide to the impairment calculation. The rationale for this decision should be described.

The regional grids have 1 column that includes diagnoses and five columns reflecting impairment classes. Identify the applicable diagnosis in the left-most column. The permissible class assignments (0–4) are specified in the horizontal rows. Reference the specific criteria in the row for that diagnosis to determine which class is appropriate. Above the criteria in each cell are five numbers reflecting the range of impairment associated with those specific diagnostic criteria. Each of these numbers corresponds to grades A, B, C, D, and E, with A the mildest and E the most severe. The middle value is grade C and represents a default impairment value, which typically corresponds with the impairment value assigned in prior editions of the Guides. Grades and the corresponding final impairment value are modified by the use of the adjustment grids and the net adjustment formula, as discussed above. The impairment calculation process is described in detail in Section 16.3d.

General Considerations

Instructions for using the diagnosis-based impairment grids are provided in Section 16.3, Adjustment Grid and Grade Modifiers—Non-Key Factors. The evaluator should select the most accurate diagnosis and identify the class containing that diagnosis. As previously described, the numerical value of the impairment associated with that diagnosis, located above each diagnosis, may be increased or decreased within an impairment class based upon grade modifiers, as determined using the adjustment grids as described in Section 16.3.

Prior to using the regional grids, the examiner must review Section 16.1, Section 16.2, and Section 16.3. In some cases, the class will be defined by physical examination findings or clinical study results. When this is the case, those same findings may not be used as grade modifiers to adjust the rating. Range of motion will, in some cases, serve as an alternative approach to rating impairment. It is not combined with the diagnosis-based impairment and stands alone as an impairment rating.

Clinical examples are provided in Section 16.3e. The Guides user is encouraged to read the entire chapter for a complete understanding of the impairment rating method before attempting to interpret the ratings or to perform the calculations that accompany the examples. (6^th ed, 499-500).

It is imperative that the examiner identify the most clinically accurate specific diagnosis, causally related to the injury, that results in the highest impairment. Impairment is not based on multiple diagnoses within a region.

The approach to ankle injuries is described in Section 16.2b Foot and Ankle:

The foot and ankle are defined as the region from below the mid-tibia to the toes, including all the

Bone, joint, ligamentous, and soft tissue structures encompassing the joints. Diagnoses and classes are listed as previously described. In the event that a specific diagnosis is not listed in the diagnosis-based impairment grid, Table 16-2, the examiner should identify a similar listed condition to be used as a guide to the impairment calculation. The rationale for this decision should be described.

Per Table 16-2, Foot and Ankle Regional Grid under the category of "Aethrodesis" for a "Double or triple arthrodesis" and "mild malalignment," there is a Class 2 rating with default impairment of 16% lower extremity. Grade Modifiers would modify this. Assuming Functional History of Grade Modifier 1, Physical Examination of Grade Modifier 2, and Clinical Studies of Grade Modifier 2 (or not relevant), the adjustment would be minus one, and the rating would be based on Grade B at 15% foot. Note, with rare exceptions, only one diagnosis is rated. However, in this case, it may be reasonable to combine this with the bimalleolar fracture (5% lower extremity default rating for "non-displaced with minimal findings" and/or post-traumatic arthritis, based on quantitative information on cartilage intervals).

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 We are offering a special 10% discount on all AMA Guides, Mastery Training Courses, till this Friday, May 16. Apply the discount coupon"SPECIALOFFER" while purchasing. Act now by Clicking Here.

The approach with the AMA Guides, Sixth Edition 2024, refines the approach of 2008. In this case, the most accurate and clinically relevant diagnosis is "ankle fracture with subsequent hindfoot fusion (arthrodesis)," which is consistent with the natural history of the condition, supported by the physical examination and clinical studies. Impairment is based on the diagnosis involving ankle fracture with subsequent hindfoot fusion. More about the approaches in the 2024 version will be in future learning resources and blogs.